Systematic studies of the subgenus Crewella of Ceratina (Hymenoptera, Apidae, Xylocopinae), with a revision of the species occurring in Argentina

: The subgenus Crewella Cockerell of Ceratina Latreille is found only in the Neotropical region, with maximal diversity in South America. A morphological study of the species in the subgenus led to the recognition of five species groups, based on several characteristics of the head, the first metasomal tergum, and the female sixth metasomal tergum. A key to the species-groups is presented. The following new species are described: C. dalyana from Colombia, C. amazonica , C. crassipunctata , and C. foveinasis from Peru, C. duplocarinata , C. guaranitica , and C. lobata from Argentina, C. acuminata from Brazil and Paraguay, and C. carbonaria from Argentina and Brazil. Lectotypes are designated for C. brunneipes Friese, C. diligens Smith, and C. vernoniae Schrottky. The following are new synonyms: C. brunneipes Friese, 1910 of C. maculifrons Smith, 1854, and C. gossypii var. asuncionis Strand, 1910 of C. gossypii Schrottky, 1907. A revision of the species in Argentina, with a key to species, is presented.


INTRODUCTION
The subgenus Crewella Cockerell is one of the seven subgenera of Ceratina Latreille present in the New World (Michener, 2007;Roig-Alsina, 2013). It includes large and colorful species with metallic reflections, although they are not as brightly colored as most species of the related subgenus Calloceratina Cockerell (Michener, 2007). Crewella occurs from Costa Rica to central Argentina, with maximum diversity in South America, particularly in tropical areas.
The subgenus Crewella has an elevated number of species, but no comprehensive account of it is available to date. Moure (2007) listed 37 available names in his Catalog, five of them as synonymous. Two names, C. rotundiceps Smith and C. asunciana Strand, have been removed to Neoclavicera (Roig-Alsina, 2013), and clarification of several other names awaits further study.
The aim of this contribution is to call attention to the morphological diversity within the subgenus Crewella, and to revise the species occurring in Argentina.

MATERIAL AND METHODS
The specimens studied were borrowed from the following institutions (acronyms of collections and names of the people who loaned the material are in parentheses): California Academy of Sciences, San Francisco, USA Rev. Mus. Argentino Cienc. Nat.,n.s. 24(1): 2022 The subgenus Crewella is characterized by the strongly punctate body with metallic colors, the face with yellow or white marks in both sexes, the well-developed preoccipital carina, the maxillary palpus with six segments, the pronotal collar delimited anteriorly by a continuous carina (the lateral portion of which is frequently lamellate, ending in a tooth-like projection), the fore and mid tibia each with both a dorsoapical spine and a ventroapical spine (Fig. 1B), the basitibial plate of the female indicated by a strong tooth, the presence of wax plates on the second and third metasomal sterna in females, and by the presence of graduli on the second to fourth metasomal terga and second to third metasomal sterna in both sexes.
Five species-groups can be recognized within Crewella, according to the degree of development of the juxtantennal carina, the structure of the clypeus, the structure of the first metasomal tergum, and the presence of depressions (usually a longitudinal furrow) on the female sixth metasomal tergum. These features are discussed below.
In many subgenera of Ceratina the areas that surround the antennal sockets are evenly depressed, meeting the frontal carina along the midline of the face, thus forming a biconcave interantennal prominence. In some other subgenera the prominence is more or less convex. In most species of Crewella the interantennal prominence is flattened, with steep sides ending at the mesal margin of the antennal socket. In some species, the sides of this flattened prominence are expanded laterally forming a juxtantennal carina (Fig. 1A), which hides in frontal view the mesal margin of the antennal socket. Such a carina is characteristic of the maculifrons, dalyana, and foveinasis species groups. The only species of the subgenus Crewella with a convex interantennal prominence are found within the amazonica group.
The clypeus of many Crewella bears a median longitudinal, narrow depression. This depression is present and usually distinct in species of the amazonica, titusi and foveinasis groups, weak or absent in species of the maculifrons group, and absent in C. dalyana. The apex of the clypeus in species of the maculifrons group is truncate (Fig. 12C, t), although sometimes narrowly so. An outstandingly large, concave truncation is characteristic of species of the foveinasis group (Fig. 6B, t).
The first metasomal tergum varies in several features, such as the extent and punctation of the disc, the presence or absence of a marginal zone, and the juncture of the anterior and dorsal surfaces, whether it is angulate or evenly rounded. A large disc separated from the anterior surface by a distinct angle is characteristic of the maculifrons group (Fig. 2B), while the titusi and foveinais groups have an outstandingly short disc ( Fig.  2A). A sharply delimited, depressed, impunctate, polished marginal zone is present in most species of Crewella ( Fig. 2A-B), except those of the amazonica group. Such a distinct marginal zone is rare among other subgenera of Ceratina. mouthparts, second segment of labial palpus the longest. Interantennal prominence usually without juxtantennal carina hiding mesal margin of antennal socket in frontal view ( Fig. 5A-B Diagnosis. This species stands apart in its own species group. It agrees with species of the C. maculifrons and C. foveinasis groups in the well-developed juxtantennal carina, but the clypeus is not truncate, the female sixth tergum lacks any median longitudinal impressions, and the forecoxa has a flattened, square lateral projection. The anterior surface of T1 in C. dalyana curves posteriorly in an arc merging gradually with the dorsal surface, without a clear limit between the two evenly punctate areas. Outstanding features of this species are the presence of a genal tubercle (Fig. 3C), the concave hypostomal area, the reduced ocelli ( Fig. 3B), the mesopleuron forming anteriorly an omaular ridge, and the red metasoma. The genal yellow band is as long as the eye, curving dorsally into the vertex (Fig. 3A). Female. Length,.5 mm (holotype 9.1 mm); length of forewing, 6.9-7.1 mm (holotype 6.9 mm). Color. Head and mesosoma black, with dark blue metallic tints; antenna with scape, pedicel and first flagellomere red, other flagellomeres dark brown; apex of clypeus and base of labrum brownish; legs dark brown, coxae and forefemur with dark blue metallic tints, distotarsi and tibial spurs yellowish brown; metasoma red, except T1 dorsally with dark blue metallic tints and T5-T6 blackened medially. Following parts yellow: clypeus with large, roughly triangular mark occupying apical 0.5-0.7 of clypeus; paraocular area with long mark, from lateral lower angle of clypeus to upper level of antennal socket; gena with yellow stripe 0.9-1.1x as long as eye, curving dorsally into vertex; forefemur with apical spot, and foretibia with basal spot followed by longitudinal dorsal stripe.

C. amazonica species group
Species of this group are characterized by the lack of a depressed, polished marginal zone on T1, present in all other groups of Crewella. The punctate disc of T1 is long, approximately twice as long as MOD, and the juncture between the anterior and dorsal surfaces is evenly rounded. The interantennal prominence is convex or rather flattened, but not as flat as in the other groups. The apical margin of the clypeus is simple, not truncate. The forecoxa has a rounded lateral projection, and the female T6 lacks a median longitudinal furrow. Species of this group are rather small, 5.5-6.5 mm long. Besides the two species from Peru described below, I have seen undescribed species from Bolivia and Colombia (preserved in IFML), each represented by only one specimen. I prefer to wait for more material to characterize these species.

C. titusi species-group
In this group the interantennal prominence is broadened, more or less flattened, but with steep sides that do not hide the mesal margin of the antennal socket in frontal view. The clypeus has the apical margin simple, not truncate. The disc of T1 bears few or no punctures, and is ex- tremely short, as long as or shorter than the posterior polished marginal zone ( Fig. 2A), which is approximately as long as MOD. The lateral projection of the forecoxa is frequently flattened and squarish, but rounded in some species. The female T6 lacks a median longitudinal furrow. Many species have long mouthparts. In these species the second segment of the labial palpus is the longest. Besides the three species treated below, in this group also belong C. bicolorata Smith, C. longiceps Smith, and C. pubescens Smith, all described from Ega, Brazil, and C. glossata Michener described from Canal Zone, Panamá. Diagnosis. This species is closely related to C. glossata by the long mouthparts, the dentate hypostomal carina, and the flattened, squarish lateral projection of the forecoxa. The two species also have a rounded tumescence on the frons at each side of the frontal carina, similar to that of species of the subgenus Zadontomerus, but punctate, not polished as in the latter.

Ceratina (Crewella) titusi
Female. Length, 8.5-9.6 mm; length of forewing, 6.8-7.5 mm. Color. Black, specimen from Iguazú, Argentina, with greenish metallic reflections on pronotal collar, dorsal area of metapostnotum and metasomal terga. Legs with ferruginous distotarsi and black tibial spurs. Following marks yellow: clypeus with median triangular longitudinal mark occupying apical 0.6-0.8 of clypeus; paraocular area with long mark, from lateral lower angle of clypeus to level of antennal socket; gena with yellow stripe 0.7-0.8x as long as eye; forefemur with apical spot and foretibia with basal spot followed by longitudinal dorsal stripe (these marks darkened in the holotype). Tegula dark brown. Wings infuscate with veins and pterostigma dark brown. Structure. Clypeus weakly convex in lateral view, without apical truncation, with shallow median longitudinal impression; median longitudinal area finely   Cockerell (1903) in the original description. Cockerell also mentioned that the mandible was produced into a tooth beneath. No such tooth was found upon examination of the holotype; probably Cockerell misinterpreted the anterior enlargement of the hypostomal carina as a projection of the mandible. The specimens studied from Misiones, Argentina, have the mouthparts somewhat shorter than those of the holotype from Guyana, and the yellow genal stripe is much broader. Apart from these differences, the specimens are nearly identical.
The brief original description of C. punctulata Spinola (1841), described from French Guiana, is very suggestive of this species. Probably C. titusi may become a junior synonym, but the type of C. punctulata was not available for study.
The anterior elevation of the hypostomal carina readily separates C. titusi from the closely related C. pubescens, which has golden reflections and a hypostomal carina of uniform height. Diagnosis. This species is characterized by the extremely short disc of T1, reduced to a sharp ridge with a few indistinct punctures medially, the short mouthparts, and the red color of the scape, pedicel and proximal three flagellomeres. It is closely related to C. bicolorata, from which it is differentiated by the smaller punctures of the head and scutum, and the coloration of the antennae. Female. Length, 7.2-8.0 mm; length of forewing, 5.8-6.2 mm. Color. Black, with green metallic tints on head, sides of T3, entire T4-T6 and S4-S6; on face with purplish reflections in part; T2-T3 with purpureous tints. Antenna with scape, pedicel and proximal three flagellomeres red. Following marks yellow: clypeus with apical, median mark frequently notched basally; paraocular area with large triangular mark close to lateral lower angle of clypeus; gena with narrow yellow stripe 0.3-0.5x as long as eye; forefemur with or without apical spot and foretibia with or without basal spot. Foretibia partly reddish, tibial spurs reddish. Tegula brown. Wings infuscate, darker along costal margin; veins and pterostigma dark brown. Structure. Clypeus straight in lateral view, with short apical truncation, 0.07-0.10x as long as length of clypeus, with distinct median longitudinal impression; at each side of impression without punctures and finely granulate. Labrum 0.7x as long as basal width; with basal convexity at each side of middle, and two median preapical small tubercles. Hypostomal carina not elevated, of uniform height. Proportion between length of eye and length of second segment of labial palpus 1:0.9. Preoccipital carina simple behind ocelli. Distance between lateral ocellus and preoccipital carina 2.3-2.5 times MOD. First flagellomere 1.3x as long as its apical width. Lateral carina of pronotum lamellate, forming lower tooth. Dorsal area of metapostnotum granulose, basally with short, longitudinal rugae; medially with single longitudinal carinula. Center of lateral part of mesopleuron with hairs short, 0.4-0.6x MOD. Lateral angle of hind coxa rounded. Hind tibial spine on basal 0.4 of tibial length. Anterior surface of T1 with few, sparse punctures; disc of T1 reduced to transverse ridge bearing few punctures; marginal zone impunctate, polished, medially as long as MOD. Apical margin of T2 and T3 truncate. T4-T5 rugose between punctures. T4-T5 with very short setae, on T5 0.3-0.4x MOD. S6 without impunctate median areas. Male. Length, 7.0 mm; length of forewing, 5.7 mm. Color. Similar to that of female, with following parts yellow: paraocular area with large triangular mark close to lateral lower angle of clypeus, median triangular mark on apical third of clypeus, basal mark on labrum, small antero-basal mark on mandible, short genal stripe, apical spot on forefemur, and basal spot followed by longitudinal stripe on foretibia. Structure. First flagellomere as long as its apical width. Median ocellus in frontal view above upper tangent of eyes. Apical margin of T7 medially, weakly emarginate. Metasomal sterna strongly punctate. S6 (Fig. 14F). Comments. The specimen designated as lectotype bears a label "this is the holotype / F. Moure 1957." Since in the original description Schrottky mentions that the species varied in length from 8.2 to 8.8 mm, it is clear that he examined more than one specimen. Consequently, a lectotype is designated. Distribution. Argentina, province of Misiones. Brazil, state of Rio de Janeiro. Paraguay, department of Alto Paraná. Material studied. Argentina. Misiones: 1 F, Cataratas Iguazú, 9-VII-1973

C. foveinasis species-group
Species in this group have a juxtantennal carina which hides the mesal margin of the antennal socket, as in the C. maculifrons group. The large, concave, polished clypeal truncation is distinctive, 0.19-0.27x as long as the clypeus (Fig.  6B, t). The labrum on the basal third is impunctate, polished, and has a single median tubercle. The disc of T1 is short, at most 1.5x as long as the posterior polished marginal zone. The forecoxa has a rounded lateral projection. The female T6 is strongly rugose, with a poorly defined median longitudinal furrow. Known species have long mouthparts, with the first segment of the labial palpus the longest. Besides the species described below, C. cupreiventris Smith (described from Ega, Brazil) also belongs in the group.

C. maculifrons species-group
This group is readily recognized by the developed juxtantennal carina, which hides, in frontal view, the mesal margin of the antennal socket (Fig. 1A, jc). The clypeus is truncate apically, the truncation being 0.08-0.23 times as long as the length of the clypeus (Fig. 12C, t). The dorsal surface of T1 is densely punctate, the disc being long, several times (2.5-5.0) longer than the posterior polished marginal zone (Fig. 2B, mz), and usually forming a distinct angle with the punctate anterior surface of the tergum, from which it is separated by a transverse, polished, impunctate low rim. The female sixth tergum bears a median longitudinal furrow, much impressed in most species (Fig. 13G), rather weak in C. diligens, C. guaranitica, and C. lobata, and enormous in C. paraguayensis (Fig. 13F). All studied species have short mouthparts and a short, rounded lateral projection of the forecoxa. Besides the eleven species treated below, C. aspera Schrottky (described from São Paulo, Brazil) and C. chrysocephala Cockerell (described from Manaos, Brazil) also belong in the group. Diagnosis. This species is readily distinguished in both sexes by the sharply pointed lateral angle of the hind coxa (Fig. 13E), and the dorsoapically compressed hind femur. The face has cupreous metallic tints as in C. morrensis, but the scape, pedicel and first flagellomere are black ( Fig.  7A Holmberg, 1903: 434. Schrottky, 1907a1907b: 477-479, 480;1913: 252. Strand, 1909: 504. Ducke, 1910. Misidentifications. Ceratina (Crewella) diligens: Moure, 2007: 643. Diagnosis. This species is readily distinguished by the double preoccipital carina in both sexes (Fig. 8A, dc), and the convex profile of the sixth sternum of the female. Males have the apical margin of T7 laterally weakly to strongly notched ( Fig. 14A-B). This species is smaller than most species of the maculifrons group of Crewella, with some males as small as 4.8 mm long. Female. Length, 6.3-8.5 mm (lectotype 8.0 mm); length of forewing, 4.9-6.0 mm (lectotype approx. 5.4 mm, tattered wings). Color. Black, with metallic tints on head, mesosoma and metasoma varying from olive-green to blue. Some blue specimens with discs of metasomal terga black, shiny, without metallic tints. Face with five yellow spots: clypeus with apical, median mark, and each paraocular area with two marks, one close to lateral lower angle of clypeus and another one bordering eye from level of upper margin of clypeus to antennal socket. Lectotype with small yellow mark on labrum; all other examined specimens with labrum black. Gena with yellow stripe 0.3-0.7x as long as eye. Legs with coxae, trochanters and femora black; tibiae and basitarsi variable, from yellowish brown (as in lectotype) to black; distal tarsomeres always paler than basitarsus; tibial spurs reddish brown; forefemur with apical yellow spot; foretibia with basal yellow spot followed by yellow stripe; middle tibia with basal yellow spot and hind tibia usually with ferruginous basal spot. Tegula dark brown to black. Wings weakly infuscate; forewing darker on costal half of marginal cell; veins and pterostigma brown. Structure. Clypeus in lateral view weakly convex; apical truncation short, 0.08-0.12 x as long as length of clypeus, in some specimens poorly defined medially. Clypeus without median longitudinal furrow or impression; reticulated between and within large, close punctures. Labrum 0.62-0.64x as long as basal width; with two short, preapical, longitudinal carinulae. Hypostomal carina low, of uniform height. Proportion between length of eye and length of second segment of labial palpus 1:1.0-1.1. Preoccipital carina double behind ocelli. Distance between lateral ocellus and preoccipital carina 1.9-2.2 times MOD. First flagellomere 1.0-1.1x as long as its apical width. Lateral carina of pronotum strong, forming lower tooth. Dorsal area of metapostnotum rugulose, basally with short, longitudinal rugae. Center of lateral part of mesopleuron with hairs 0.7-1.3x MOD, with very short branches. Lateral angle of hind coxa rounded. Hind tibial spine on basal 0.33 of tibial length. T1 with anterior surface and disc densely punctate. Apical margin of T2 laterally rounded, medially rounded to briefly truncate; apical margin of T3 rounded. T4 rugose on apical 0.15-0.20; disc with integument flat between punctures; T5 variable, similar to T4 to rugose on apical 0.75. T4-T5 with very short, pointed setae, scarcely longer on T5 (0.2-0.3x MOD). T6 with longitudinal median impression. S6 with median longitudinal impunctate keel; sternum convex in lateral view. Male. Length, 4.8-6.3 mm; length of forewing 4.1-4.5 mm. Color. Similar to that of female, with following parts yellow: narrow paraocular band from lower lateral angle of clypeus to level of antennal socket; transverse spot on apex of clypeus; spot on base of mandible; median, basal spot on labrum; genal stripe; marks on legs variable, usually forefemur with apical spot, foretibia and forebasitarsus with dorsal stripe on entire length, and basal spot on middle tibia; some specimens also with yellow spot on hind tibia, and others with legs mostly black, with yellow marks reduced to those on forefemur and tibia. Structure. First flagellomere 0.8-0.9x as long as its apical width. Median ocellus in frontal view above upper tangent of eyes. Apical margin of T7 medially weakly emarginate, laterally from sinuous to distinctly notched. Discs of S3-S5 punc-tate. S6 (Fig. 14C). Comments. A lectotype is designated, since at least two specimens of this species from the Smith collection are preserved at NHMUK. Smith (1879) did not indicate the number of specimens studied. The lectotype bears the following labels: "Type" (round label bordered with red); "B.M. Type / Hym / 17B 329;" "Ceratina / diligens / Type Sm." (handwritten); "Santar / em" (round label), "54 / 63" (round label). The second specimen, also from Santarem, Smith Collection 79-22, is designated as paralectotype.
This species has not been properly recognized by subsequent authors, as indicated in the synonymy above. Schrottky (1907b: 477-470) redescribed it in detail under the name C. maculifrons, and his misidentification was followed by Strand (1909Strand ( , 1910. Ducke (1910) erroneously synonymized C. diligens under C. maculifrons.
The margins of the double preoccipital carina behind the ocelli can be close together in some specimens, while in other specimens they may be separated by a considerable intervening space, as in Fig. 8A. The lateral portion of the apical margin of T7 of the males varies from being just sinuous to having a distinct, sharp notch. This variation can be observed among specimens from the same location, as in those from Iguazú National Park, Province of Misiones, Argentina, figured here (Fig. 14A-B). Most specimens in Argentinean populations bear a well-defined notch. The tibiae and basal tarsomeres are usually dark brown to black, but specimens with pale yellowish-brown tibiae and tarsi are found in series collected in the same place at the same time, where both types of coloration are observed. Distribution. Argentina, provinces of Chaco, Corrientes, Formosa, Misiones, Salta, and Santa Fe. Brazil, states of Minas Gerais, Pará, and São Paulo. Paraguay, departments of Asunción, Diagnosis. This species is distinguished by the reduced lateral carina of the pronotum, the short clypeal truncation, and the extended yellow markings in both sexes, including a yellow spot on the posterior margin of the pronotal lobe in most specimens. A yellow mark on the pronotal lobe is also present in C. paraguayensis, but in this species the entire posterior half of the lobe is yellow. Males of C. gossypii have a yellow stripe on the dorsal surface of the foretibia and on the forebasitarsus, and the basal spot on the hind tibia usually reaches the basitibial spine. Females may have the yellow paraocular mark entire or divided in two. Female. Length, 7.0-9.7 mm; length of forewing, 5.2-7.1 mm. Color. Black, with metallic tints on head, mesosoma and metasoma varying from olive-green to blue. Face usually with three yellow spots: clypeus with apical, median mark, and paraocular area with large mark bordering eye, broadest close to lateral margin of clypeus and narrow above, frequently constricted at level of upper margin of clypeus; some specimens with paraocular mark split in two, so face with five yellow marks. Gena with yellow stripe 0.5-0.7x as long as eye. Pronotal lobe frequently with yellow spot on posterior margin, sometimes small or absent. Forefemur with apical yellow spot; foretibia with basal yellow spot followed by yellow stripe; middle tibia with basal yellow spot and hind tibia with yellow spot at least half as long as basitibial area and usually reaching basitibial spine; tibial spurs and distal tarsomeres reddish brown. Tegula brown to dark brown. Wings infuscate, with brown veins and pterostigma. Structure. Clypeus straight in lateral view, reticulated between and within large punctures; apical truncation short, 0.06-0.13x as long as length of clypeus. Clypeus usually without median longitudinal impression, but few specimens with such impression weakly indicated. Labrum 0.6x as long as basal width, strongly punctate, with median longitudinal depression and two preapical, short, longitudinal carinulae. Hypostomal carina low, of uniform height. Proportion between length of eye and length of second segment of labial palpus 1:0.95-1.05. Preoccipital carina simple behind ocelli. Distance between lateral ocellus and preoccipital carina 2.2-2.7 times MOD. First flagellomere 1.2x as long as its apical width. Lateral carina of pronotum low, frequently carinate, but shortly lamellate in some specimens. Dorsal area of metapostnotum finely granulose, basally with short, longitudinal rugae. Center of lateral part of mesopleuron with hairs 0.7-1.1x MOD, with distinct branches. Lateral angle of hind coxa broadly rounded (Fig. 13C) to narrowly rounded (as in Fig. 13D). Hind tibial spine on basal 0.33 of tibial length. T1 with disc densely punctate. Apical margin of T2 and T3 rounded. T4 rugose on apical 0.15-0.30; disc with integument flat between punctures; T5 rugose. T4-T5 with very short, decumbent setae with rounded apices, those on T5 as long as 0.3-0.5x MOD. T6 with median longitudinal furrow. S6 with median longitudinal impunctate keel; sternum straight in lateral view. Male. Length, 7.0-7.8 mm; length of forewing 5.3-6.2 mm. Color. Similar to that of female, with following parts yellow: paraocular band from lower lateral angle of clypeus to level of antennal socket; transverse spot on apex of clypeus; spot on base of mandible; median, basal spot on labrum; genal stripe; frequently with spot on posterior margin of pronotal lobe; forefemur with apical spot, foretibia and forebasitarsus with dorsal stripe usually on entire length; basal spot on middle and hind tibiae, spot on hind tibia usually reaching basitibial spine. Structure. First flagellomere 1.2x as long as its apical width. Median ocellus in frontal view above upper tangent of eyes. Apical margin of T7 entire, medially weakly emarginate. Discs of S3-S5 punctate. S6 (Fig. 14I). Comments. Schrottky's detailed description (1907b) allows the identification of this taxon with certainty, in spite of the loss of the type. The holotype had green metallic tints, as most specimens studied from Formosa and Corrientes in Argentina, but other specimens are bright blue, a color variation also observed in C. maculifrons and C. diligens. Strand (1910) studied specimens of C. gossypii from Villa Morra and Asunción (Paraguay), and described the variety asuncionis for five females from Asunción with the paraocular mark divided in two. The extent of the paraocular yellow mark varies in C. gossypii from a single broad mark to two small, well separated spots. This variation occurs in specimens from the same population.
This species is closely related to C. maculifrons, from which it differs in several details. Both taxa have the same color variation, from metallic olive-green to blue, and have the same pattern of yellow markings, presenting specimens with three or five marks on the face. Ceratina gossypii has a narrower clypeal truncation, the clypeus usually lacks a median longitudinal impression (but few specimens have such impression weakly indicated), the lateral carina of the pronotum is weaker, in most specimens much reduced at the level of the transpronotal groove, the setae on the disc of T5 are prostrate, short, and with broad apices (Fig. 8B-C), the pilosity of the mesopleuron is more plumose, and the labrum more strongly punctate. Specimens of C. maculifrons have a clypeal truncation 0.16-0.22x as long as the length of the clypeus, a distinct median longitudinal impression on the clypeus, a lamellate, strong lateral carina on the pronotum, erect, pointed setae on the disc of T5, pilosity on the mesopleuron below the hypoepimeral area with hairs simple or with short branches, and the labrum basally mostly polished, with small punctures. These differences hold between the studied specimens from northern Argentina, Bolivia and Paraguay (C. gossypii), and those from the Amazonian region (C. maculifrons), and I keep them as separate species, but further study of material from intervening areas may show that this is just clinal variation, and that C. gossypii is a junior synonym of C. maculifrons. Distribution. Argentina, provinces of Chaco, Diagnosis. This species is distinguished by the granulose dorsal area of the metapostnotum, the truncate apical margin of T2 and T3, the reduced apical truncation of the female clypeus, and the shallow longitudinal impression of the female T6, which is accompanied by a lateral depression at each side of it. The face bears cupreous metallic reflections, as in C. morrensis, from which it is readily distinguished by the black antennae and the longer pubescence on the mesopleuron. Female. Length, 8.5-9.5 mm (holotype 9.0 mm); length of forewing, 6.6-7.3 mm (holotype 6.6 mm). Color. Black, with metallic color tints: bronzy-green on head and metasoma, on face with cupreous reflections on upper half, several specimens also with some cupreous reflections on metasomal terga (more pronounced on T1-T3) and sterna; bronzy-green also on dorsum of pronotum, perimeter of scutum, scutellum and metanotum; pleurae with bluish tints; dorsal area of metapostnotum and propodeum without metallic reflections. Face with five yellow spots: clypeus with apical, median mark, and each paraocular area with two marks, one close to lateral lower angle of clypeus and another one bordering eye from level of upper margin of clypeus to antennal socket. Gena with yellow stripe 0.7-0.85x as long as eye. Forefemur with apical yellow spot; foretibia with basal yellow spot followed by yellow stripe; tibial spurs reddish brown. First flagellomere 0.8x as long as its apical width. Median ocellus in frontal view above upper tangent of eyes. Apical margin of T7 entire, medially weakly emarginate. Discs of S3-S5 punctate. S6 (Fig. 14J). Etymology. The specific name refers to the region where the species occurs, the Guaraní department in the province of Misiones. of the female is also diagnostic, bearing a median longitudinal furrow (Fig. 10B). Female. Length, 8.0-9.0 mm (holotype 9.0 mm); length of forewing, 6.7-7.1 mm (holotype 7.1 mm). Color. Black, with metallic color tints: dark blue on head and mesosoma, reddish on frons and interantennal area, and bright olive-green on metasoma. Clypeus with apical, median, small yellow mark; paraocular area with single yellow mark close to lateral lower angle of clypeus; gena with yellow stripe 0.6-0.75x as long as eye. Legs black with reddish distotarsi; forefemur with or without apical yellow spot; foretibia with basal yellow spot; tibial spurs reddish.  Ducke, 1910: 363. Diagnosis. This species is distinguished by the extended yellow markings in both sexes, including a yellow spot on the posterior margin of the pronotal lobe in most specimens. All tibiae have a yellow basal spot, that on the hind tibia usually reaching, and sometimes surpassing, the basitibial spine. Males have a yellow stripe on the dorsal surfaces of the foretibia and the forebasitarsus. Females may have the yellow paraocular mark entire or divided in two. Two other species have extended yellow markings: C. paraguayensis and C. gossypii. Ceratina maculifrons is readily differentiated from the former by the weakly infuscate wings with brown veins and pterostigma, and the narrow longitudinal furrow on the female T6. Ceratina paraguayensis has bright yellowish-brown wings, with yellowish veins and pterostigma, and the costal sclerite of the forewing bears a yellow spot. Differences with C. gossypii are discussed under that species. Comments. Ceratina maculifrons would run to C. gossypii in the key to species of Argentina below, except that the lateral carina of the pronotum is lamellate, not low and carinate. Other differences between these two morphologically very similar species are discussed above under C. gossypii. Specimens of C. maculifrons vary in the color of the integument from metallic olive-green to distinctly metallic blue, and the paraocular yellow mark of the female varies from entire to divide into two spots. The name C. maculifrons Smith (1854) has been used by subsequent authors to refer to different species. The citations of Holmberg (1903), Schrottky (1907aSchrottky ( , b, 1913 and Strand (1909Strand ( , 1910 correspond to specimens of C. diligens. The usage of the name by other authors needs further clarification. The specimen selected as lectotype of C. brunneipes, a female from Obidos, agrees in all morphological details with the type of C. maculifrons. The reddish coloration of the pale markings suggests that the lectotype was collected with cyanide. Two specimens collected by Ducke in Pará (17.IX.1899 and6.XII.1899), preserved in CAS, were identified by him as C. punctiventris Friese. These specimens are probably part of the same series from Pará sent by Ducke to Friese, and used by the latter author for his description of C. punctiventris. The two specimens agree in detail with Friese's description, and I take Ducke's synonymy of this name under C. maculifrons as correct.  Ceratina morrensis Strand, 1910: 504-505 (syntypes female and male, Villa Morra and Trinidad, Paraguay, ZMB, not examined). Cockerell, 1919:176. Strand, 1912: 267. Ceratina morrensis var. cuprifrons Strand, 1910 (syntypes, female, Villa Morra, Paraguay, ZMB, not examined). Cockerell, 1919: 176. Ceratina (Crewella) morrensis: Moure, 2007: 644. Diagnosis. This species is readily distinguished by the red color of the scape, pedicel, and proximal flagellomeres. The only other species in the area with this color pattern is C. vernoniae, of the C. titusi species-group. Also characteristic of both sexes of C. morrensis are the profuse cupreous tints on the head and thorax, the infuscate wings, being the costal half of the marginal cell darker, and the narrowly rounded (Fig. 13D) to briefly pointed lateral angle of the hind coxa. The hairs on the center of the lateral part of the mesopleuron are very short, distinctly shorter than those on the anterior margin and those close to the metapleuron. This type of pilosity separates C. morrensis from C. acuminata and C. guaranitica, which may also have cupreous tints, but their pilosity on the mesopleuron is of even length. Female. Length,.0 mm; length of forewing, 6.2-8.5 mm. Color. Black, with various amounts of green and cupreous metallic tints. Face with greenish tints and curpeous color restricted to areas around ocelli and antennal sockets, to face entirely cupreous; pronotum with cupreous tints restricted to anterior and dorsal surfaces, to entirely cupreous; scutum and scutellum with cupreous tints on the perimeter; metanotum, propodeum and metasoma usually with greenish tints, but many specimens with metasoma black, shiny, without metallic tints (see comments below). Antenna with scape, pedicel, and proximal two to three flagellomeres red. Face with three yellow spots: clypeus with apical, median mark, and paraocular area with large mark bordering eye, broadest close to lateral margin of clypeus and narrow above, usually constricted at level of upper margin of clypeus; few specimes with paraocular mark split in two, so face with five yellow marks. Gena with yellow stripe 0.7-0.8x as long as eye. Forefemur with apical yellow spot; foretibia with basal yellow spot followed by yellow to ferruginous stripe; middle tibia with basal yellow to ferruginous spot; hind tibia with ferruginous basal mark, usually extending to, or surpassing, basitibial spine. Tegula brown. Wings infuscate; forewing darker on costal half of marginal cell; veins and pterostigma brown. Structure. Clypeus in lateral view weakly convex; apical truncation 0.10-0.17x as long as length of clypeus. Clypeus without median longitudinal furrow or impression; reticulated between and within large punctures. Labrum 0.69-0.72x as long as basal width; with two short, preapical, longitudinal carinulae. Hypostomal carina low, of uniform height. Proportion between length of eye and length of second segment of labial palpus 1:1.0-1.1. Preoccipital carina simple behind ocelli. Distance between lateral ocellus and preoccipital carina 2.4-2.8 times MOD. First flagellomere 1.0-1.1x as long as its apical width. Lateral carina of pronotum strong, forming lower tooth. Dorsal area of metapostnotum rugulose, granulose in some specimens, basally with short, longitudinal rugae. Center of lateral part of mesopleuron with hairs 0.4-0.8x MOD, shorter than hairs close to mesopleuron. Lateral angle of hind coxa narrowly rounded to briefly pointed. Hind tibial spine on basal 0.33 of tibial length. T1 with anterior surface and disc densely punctate. Apical margins of T2 and T3 laterally rounded, medially rounded to briefly truncate. T4 rugose on apical 0.15-0.20; disc with integument flat between punctures; T5 variable, similar to T4 to entirely rugose. T4-T5 with very short, erect, pointed setae, on T5 0.3-0.4x MOD. T6 with longitudinal median furrow. S6 with median longitudinal impunctate keel; sternum straight in lateral view. Male. Length, mm; length of forewing 6.2-6.8 mm. Color. Similar to that of female, with following parts yellow: large paraocular band occupying entire lower part of paraocular area to upper level of clypeus, tapering then up to level of antennal socket; triangular mark on apex of clypeus; anterior spot on outer surface of mandible; median, basal spot on labrum; genal stripe; forefemur with apical spot; foretibia with basal spot followed by dorsal stripe; middle tibia without o with small spot. Hind tibia ferruginous basally. Structure. First flagellomere 0.8x as long as its apical width. Median ocellus in frontal view above upper tangent of eyes. Apical margin of T7 entire, medially weakly emarginate. Discs of S3-S5 punctate. S6 (Fig. 14L). Comments. Specimens studied from Parque Nacional Iguazú, province of Misiones, all have an entirely black metasoma, while most specimens from northwest and north-central Argentina have the metasoma with metallic green tints. The two types of coloration are found among specimens from other localities of Misiones (Loreto and San Ignacio), of Formosa (Reserva El Bagual), and of Entre Ríos (Liebig). Of over a hundred and fifty studied specimens, only three have been found with an intermediate coloration: T2-T3 or T2-T4 black and other terga and sterna greenish, although green not as bright as in all-green specimens. No morphological differences are seen between these two color morphs. This color variation was already mentioned by Cockerell (1919).
The types were not examined, but Strand's detailed original description of C. morrensis allows the identification of the species with certainty. The variety cuprifrons was proposed by Strand for specimens from the same locality (Villa Morra), but with more extensive cupreous tints.
Diagnosis. This species is readily distinguished by the large impression of the female T6, in the form of an inverted triangle (Fig. 13F), by the yellowish-brown wings, and by the extended yellow markings in both sexes, being the pronotal lobe yellow on the rear half. Female. Length,.0 mm; length of forewing, 6.7-7.6 mm. Color. Black, with dark blue metallic tints on head and mesosoma, and bronzygreen tints on metasoma; some specimens with cupreous reflections on frons and discs of metasomal terga. Face with three yellow spots: clypeus with apical, median mark, and paraocular area with large mark bordering eye, broadest close to lateral margin of clypeus and tapering above to level of antennal socket. Gena with yellow stripe 0.5-0.7x as long as eye. Pronotal lobe and costal sclerite of forewing with yellow spot. Forefemur with apical yellow spot; foretibia with basal yellow spot followed by yellow stripe; middle and hind tibiae with yellow spot, that on hind tibia usually reaching or surpassing basitibial spine; tibial spurs and distal tarsomeres reddish brown; Tegula yellowish brown. Wings pale, yellowish brown; veins and pterostigma yellowish brown. Structure. Clypeus in lateral view with raised apex; apical truncation short, 0.10-0.15x as long as length of clypeus. Clypeus without median longitudinal furrow or impression; reticulated between and within large punctures. Labrum convex, 0.6x as long as basal width; with reduced preapical, longitudinal carinulae. Hypostomal carina low, of uniform height. Proportion between length of eye and length of second segment of labial palpus 1:1.05. Preoccipital carina simple behind ocelli. Distance between lateral ocellus and preoccipital carina 2.2-2.4 times MOD. First flagellomere 1.0-1.1x as long as its apical width. Lateral carina of pronotum low close to transpronotal groove, becoming stronger below. Dorsal area of metapostnotum granulose, basally with short, longitudinal rugae. Center of lateral part of mesopleuron with hairs 0.5-0.8x MOD, with very short branches. Lateral angle of hind coxa rounded. Hind tibial spine on basal 0.33 of tibial length. T1 with disc densely punctate. Apical margin of T2 and T3 laterally rounded, medially truncate. T4 rugose apically, on 0.15-0.20 of its length; disc with integument flat between punctures; T5 strongly rugose. T4-T5 with very short setae, those on T4 not sticking out of punctures, on T5 as long as 0.4-0.5x MOD. T6 with large median triangular impression. S6 with median longitudinal impunctate keel; sternum straight in lateral view. Male. Length, 8.5 mm; length of forewing 6.2 mm. Color. Similar to that of female, with following parts yellow: large paraocular band occupying entire lower part of paraocular area to upper level of clypeus, tapering then up to level of antennal socket; large, transverse mark on apex of clypeus; large basal spot on outer surface of mandible; most of labrum, except apical rim; genal stripe; pronotal lobe with spot occupying rear half; forefemur with apical spot; foretibia and forebasitarsus with dorsal stripe; middle tibia with basal spot; hind tibia with yellow mark extending beyond basitibial spine. Structure. First flagellomere as long as its apical width. Median ocellus in frontal view above upper tangent of eyes. Apical margin of T7 entire, medially weakly emarginate. Discs of S3-S5 punctate. S6 (Fig. 14M). Distribution. Argentina, provinces of Chaco, Corrientes, Formosa, and Misiones. Brazil Diagnosis. This species is readily distinguished by the intense blue color of the body, the reduced yellow marks, the raised preapical margin of the clypeus, and the long first flagellomere (Fig.  11E-F). The punctation is denser, and the punctures smaller (Fig. 13B), than in other species of the C. maculifrons group, except C. sericea. Males are readily distinguished by the medially pointed apical margin of T7, the enlarged compound eyes, and the narrow, depressed frons, the median ocellus in frontal view lying below the upper tangent of the compound eyes (Fig. 11F). Female. Length, 7.5-12.5 mm; length of forewing, 6.0-9.2 mm. Color. Head, mesosoma and metasoma metallic blue, except following parts black: antennae, sides of clypeus, labrum, mandibles, polished area of scutum, and pregradular areas of terga and sterna; some specimens with scarce purple reflections on face and pleurae. Face with small yellow spot on lower corner of paraocular area, but some specimens also with small yellow spot on apex of clypeus. Gena with yellow stripe 0.35-0.45x as long as eye. Legs with coxae, trochanters and femora with blue reflections; tibiae and tarsi black, except ferruginous distotarsi; forefemur with apical yellow spot and foretibia with small basal yellow spot; middle and hind tibiae with or without small basal yellow spot. Tegula dark brown to black. Wings infuscate; veins and pterostigma brown. Structure. Clypeus in lateral view straight basal-ly, but apically concave due to distinctly raised preapical margin; apical truncation 0.10-0.15x as long as clypeus. Clypeus without median longitudinal furrow or impression; reticulated between and within close punctures (separated by 0.2-0.3 PD). Labrum 0.57-0.62x as long as basal width; with two short, preapical, longitudinal carinulae. Hypostomal carina low, of uniform height. Proportion between length of eye and length of second segment of labial palpus 1:0.8-0.9. Preoccipital carina simple behind ocelli. Distance between lateral ocellus and preoccipital carina 2.3 times MOD. First flagellomere 1.75-1.80x as long as its apical width. Lateral carina of pronotum low, not forming lower tooth. Dorsal area of metapostnotum granulose, basally with short, longitudinal rugae. Center of lateral part of mesopleuron with hairs 0.3-0.4x MOD. Lateral angle of hind coxa rounded. Hind tibial spine on basal 0.28-0.30 of tibial length. T1 with disc densely punctate. Apical margin of T2 and T3 briefly truncate. T4 rugose on apical 0.20-0.75, basally with integument flat between punctures; T5 rugose. T4-T5 with short, decumbent setae with rounded apices, on T5 0.3-0.5x MOD. T6 with longitudinal median furrow. S6 with median longitudinal, impunctate, low keel; sternum straight in lateral view. Male. Length, 7.7-10.0 mm; length of forewing 6.2-8.2 mm. Color. Similar to that of female, with following parts yellow: narrow paraocular band from lower lateral angle of clypeus to level of antennal socket; transverse spot on apex of clypeus; anterior spot on outer surface of mandible; median, basal spot on labrum; genal stripe; forefemur with apical spot, foretibia with basal spot followed by dorsal stripe; middle and hind tibiae without or with small basal spot. Structure. First flagellomere 1.8-2.0x as long as its apical width. Median ocellus in frontal view below upper tangent of eyes. Apical margin of T7 entire, medially with pointed projection. Discs of S3-S5 with smooth impunctate median area. S6 (Fig. 14N).  1.-T1 with disc short, as long as, or shorter than posterior polished marginal zone (as in Fig.  2A). Interantennal prominence not hiding mesal margin of antennal socket in frontal view (Fig. 5D) Fig. 8A). Apical margin of T7 frequently with lateral sinuosity or notch (Fig. 14A-B