Boreocanthon Halffter 1958
Creators: name: Edmonds, W. D.
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Scarabaeidae
Boreocanthon

description: Genus Boreocanthon Halffter, 1958, restored generic status
Boreocanthon Halffter 1958: 208 (as genus)
Canthon (Boreocanthon Halffter) (downgraded to subgenus of Canthon Hoffmannsegg per Halffter and Martínez 1977: 81)
Type species. Ateuchus ebenus Say, 1823, by original designation (as Canthon ebenus [Say]).
Summary diagnosis. North American dung beetles, ball-rolling species attracted to a wide range of animal feces; usually dark or black in color, small-sized (length usually 4–7 mm); head margin conspicuously quadri- or sexdentate; parameres compressed laterally, truncate apically, lacking elongate projection of lower apical angle; hind femora lacking fine carina along anterior edge; metatibia with single apical spur.
Diagnosis. Dorsum (head + pronotum + elytra + pygidium) shagreened (alutaceous), with either punctures (Fig. 38, 48, 75, 105) or raised granules (Fig. 8. 19), punctures often accompanied by field of faintly lustrous microspotting (Fig. 61, 88); pterothoracic and abdominal sclerites shagreened, usually with accompanying flattened granules or punctures. Head: Clypeus quadridentate (Fig. 20, 66, 79, 112) (sometimes virtually bidentate in B. coahuilensis, Fig. 47); paraocular areas often also angulate such that head appears sexdentate (Fig. 66, 79). Clypeal teeth reflexed, surface behind concave, finely rugose and often somewhat shinier than rest of head surface, which is usually punctate on shagreened background. Clypeal process a low, transverse ridge. Labiogular fimbria always setose, often V-shaped, usually with associated field of coarse punctures at midline (Fig. 60, 69). Prothorax: Subapical tubercle beneath anterior angle of pronotum usually absent. Hypomeral carina usually absent (Fig. 24), sometimes partially developed but never long, extending at most only one-fifth to one-quarter of distance to edge of prothorax (Fig. 40, 108, arrow). Legs: Protibia strongly tridentate, usually serrate along lateral margin and between large teeth, inner margin smoothly curved (Fig. 104) or offset at level of basal tooth (Fig. 51). Anterior tibial spurs sexually dimorphic in most species: acute apically in female (Fig. 116a), unequally bifurcate apically in male (Fig. 116b); apex acute in both sexes in B. ebenus and B. depressipennis (Fig. 16). Posterior femora not margined anteriorly. Posterior tibiae with single apical spur. Elytra: Nine elytral striae; striae superficial, not impressed, lateral margins sometimes sharpened by fine carinulae (Fig. 61, 71); 9 th (epipleural) stria, if distinct, effaced anteriorly; 8 th (subhumeral) sometimes carinulate (Fig. 88, arrow); 7 th and 8 th sometimes almost effaced anteriorly (Fig. 99). Interstriae always shagreened, either microspotted or granulate, sometimes presenting distinct humeral puncturing; anterior ends of first elytral interstriae depressed below level of second interstriae; anterior ends of 2 nd and 3 rd interstriae sometimes swollen (Fig. 67, 111), otherwise discal interstriae flattened. Genital capsule: Distal portion of parameres laterally compressed, truncate, posterior edges straight, appressed, profile varies from abbreviated (Fig. 113) to elongate triangle (Fig. 85), lacking any curved elongation of the lower apical angle (as in Fig. 43a). General: Small, length rarely over 7.5 mm, usually 4.5–6 mm. North America from Trans-Mexican Volcanic Belt in southern Mexico, through the United States into far south-central Canada (Fig. 1).
Comments. Boreocanthon is here restored to its original status of genus because, like its close relative, Melanocanthon, it exhibits a distinguishing suite of morphological features (see Diagnosis) and a plainly North American distribution. I have not discovered any unique feature (synapomorphy) that both unites its 13 species and separates them from other “ Canthon,” sensu lato, and, therefore, I cannot argue with a high degree of confidence that the group is monophyletic. Boreocanthon and Melanocanthon, along with the pilularius species-group of Canthon (sensu Halffter 1961) constitute the endemic United States contingent of the North American fauna of deltochiline Scarabaeinae. All other deltochilines occurring in temperate North America, north of the Rio Grande, are recently arrived representatives of southern groups; these include Deltochilum gibbosum (Fabricius), Pseudocanthon perplexus (LeConte), Canthon (Glyphrocanthon) viridis (Palisot de Beauvois), C. (Canthon) humectus (Say), C. (C.) indigaceus LeConte and C. (C.) cyanellus LeConte.
Boreocanthon is closely related to Melanocanthon, and the two are sometimes confused in collections. The latter group, however, is distinguished by having two apical spurs on the hind tibia (rather than one) as well as, among other features, subtle differences in dorsal sculpturing and the shape of the head and sides of the prothorax and elytra, and a distribution largely confined to the southeastern quadrant of the United States, including the eastern one-half of Texas. There are presently four recognized species of Melanocanthon, but my informal impression is that there may be but three. A future, more rigorous look at Melanocanthon is very much in order. Halffter et al. (2022) recently created the subgenus Bajacanthon to accommodate the unique Baja California endemic species, Canthon obliquus Horn. In their phylogenetic analysis (Melanocanthon was not included) the new genus emerged as sister group to Boreocanthon, with which it shares several features, especially the form of the parameres (Fig. 44a,b).
Boreocanthon is a Nearctic taxon with deep Neotropical roots. The center of diversity of the genus is clearly the United States and adjacent northern Mexico, where it undoubtedly originated. It, as well as Melanocanthon and the pilularius species group of Canthon, are the only representatives of the Neotropical tribe Deltochilini that originated and diversified in the Nearctic. The historical biogeographic perspective proposed by Kohlmann and Halffter (1990) seems reasonable in the context of the results of this study: “The ancestor of Melanocanthon - Boreocanthon would have been distributed in northern Mexico and south-central USA, while the area was covered by tropical deciduous forest. By the end of Miocene the forest started to be replaced by grasslands and piñon-oak woodland, a process that was advanced in the Pliocene by the spread of pine forest and very recently the appearance of deserts. Most Boreocanthon species … live in this area, which leads us to think that this was the main evolutionary arena for this group. Nowadays, many of the species live in grasslands of the Great Plains … or in arid zones …” (p. 13). In the context of Gonzalo Halffter’s theory of the Mexican Transition Zone (Morrone 2015; Halffter 2017; Halffter and Morrone 2017 and numerous references therein), the modern Nearctic taxa, including Boreocanthon, are the descendants of deltochilines among a wave of Neotropical immigrants that arrived in North America during early Cenozoic, where they originated and began to radiate during Miocene-Pliocene times. This early wave of taxa from the south produced the founding cenocron of Halffter’s Mexican Plateau Dispersal Pattern, one of five distribution patterns comprising the biogeographical panorama of the Mexican Transition Zone (Halffter and Morrone 2017). This cenocron included many other scarabaeines and other insects, including Phanaeus, whose biogeographical history in part parallels that of the Boreocanthon and other Nearctic deltochilines (Kohlmann and Halffter 1990; Halffter and Morrone 2017) as well as other groups (Edmonds 1994).
The distribution of the genus covers much of North America (Fig. 1). Of interest is the fact that the distributions of the member species of putative species pairs (B. ebenus-B. depressipennis, Fig. 28; B. melanus-B. forreri, Fig. 45; B. puncticollis-B. integricollis, Fig. 63; B. probus-B. halffteri, Fig. 82; and B. simplex-B. coahuilensis, Fig. 100) are allopatric or nearly so, which suggests a long history of vicariant/dispersal events punctuating the history of the group (see, for example, Gámez et al. 2016). The ecogeographic distributions of Boreocanthon species conform rather closely to the vegetation biomes depicted in Figure 2: B. depressipennis and most B. probus, to eastern coniferous open-canopy forests; B. praticola and B. ebenus, to mid-latitude steppe and prairie; B. lecontei and B. integricollis to arid south Texas shrubland; and B. simplex to the complex highly variable mosaic of biomes present west of the Rocky Mountains. Western populations of B. probus, as well as B. halffteri, have colonized west Texas / New Mexico steppe and desert shrub habitats. All the Mexican species (B. melanus, B. forreri, B. ateuchiceps, B. coahuilensis, and B. puncticollis) are associated with desert and desert shrub areas.
That the diversity hotspot for Boreocanthon lies in the southwestern portion of the United States is unsurprising in that it is the focus of diversity for numerous vertebrate and invertebrate groups (see Parmenter et al. 1995). In this complex assemblage of arid and semi-arid range and basin habitats characteristic of western Texas, and southern New Mexico and Arizona, seven species come together: B. puncticollis, B. melanus, B. ebenus, B. halffteri, B. simplex, B. praticola and B. probus. Only two, however, are endemics: B. halffteri and B. melanus. For comparison, in the United States west of the Rocky Mountains north of about 34° latitude, an area much larger than the U.S. Southwest, is home to a single, albeit highly variable species, B. simplex. All other species, B. lecontei, B. integricollis, B. depressipennis, B. coahuilensis, B. ateuchiceps and B. forreri can be considered peripheral, relatively localized relatives of these seven. What this says about the biogeographical history of the genus is ripe for analysis.
Available data bespeak a group that is fundamentally coprophagous, with but very few records of attraction to carrion and none to fungi or other decomposing organic matter. Available information suggests the group to be almost exclusively coprophagous but highly generalist in food choice. Reported dung sources include a wide variety of wild and domestic animals: humans, hog, cattle, bison, horses, burros, deer, elk, rabbit, prairie dog, fox, bear, coyote, dog, domestic cat, javelina (collared peccary), opossum, chicken. In only one known instance does a species exhibit a preference for a particular food source: B. praticola (q.v.) for dung pellets of prairie dogs (Cynomys spp.). Zunino and Halffter (2007) report several casual associations between species of Boreocanthon and various vertebrate nests: B. simplex with ground squirrel (Citellus) burrows; B. puncticollis with packrat (Neotoma) and kangaroo rat (Dipodomys) nests. Presumably, all Boreocanthon conserve the ball-making/rolling (telocoprid) strategy characteristic of deltochilines (see Tonelli 2021). While there are some anecdotal observations that they do, I know of no formal corroborative studies on the feeding and nesting behaviors of any species of Boreocanthon.
Pollock and Lavigne (2019) reported that B. praticola, along with Digitonthophagus gazella (Fabricius 1787) and Canthon floridanus Brown, 1946 (until recently known as C. imitator Brown; see Génier 2019) are regular prey items for various species of robber flies (Diptera: Asilidae) in eastern New Mexico.
Robinson (1948) presented the first modern key to the species of this genus. He included the ten thenknown species of Boreocanthon in the United States and his study heretofore has been the standard taxonomic reference for the group. Boreocanthon species group in his key to Canthon (couplets [0] through 2) on the basis of the following combination of characters: a) no [complete] hypomeral carina; b) anterior edge of hind femora not bearing a carina; and c) hind tibia with a single apical spur. As defined here, Boreocanthon embraces the thirteen valid species listed below. A total of 22 available and one unavailable species-group names, and their status as valid or otherwise, are assigned to the genus and listed below (original generic placement in parentheses; brackets enclose reference to designator; valid names and new nomenclatural actions are in bold type):
abrasus LeConte 1859c: 11 (Canthon) —jr. subj. syn. probus Germar [Horn 1870: 45]
antiguus Pierce 1946: 120 (Canthon)—jr. subj. syn. simplex LeConte [Miller et al. 1981:626]
ateuchiceps Bates 1887: 35 (Canthon) —valid name
bisignatus Balthasar 1939: 229 (Canthon) —jr. subj. syn. militaris Horn, new synonymy
coahuilensis Howden 1966: 732 (Canthon) —valid name
corvinus Harold 1868: 129 (Canthon) —jr. subj. syn. simplex LeConte [Horn 1870: 46]
depressipennis LeConte 1859c: 11 (Canthon) —valid name
ebenus Say 1823: 208 (Ateuchus) —valid name ebeneus Say 1823: 208 (Ateuchus) —suppressed (see Comments for ebenus)
forreri Bates 1887: 31 (Canthon) —valid name
halffteri Edmonds (Boreocanthon) — new species
humeralis Horn 1870: 46 (Canthon)—jr. subj. syn. simplex LeConte [Robinson 1948: 87]
integricollis Schaeffer 1915: 50 (Canthon) —valid name
lecontei Harold 1868: 68 (Canthon) —valid name
melanus Robinson 1948: 88 (Canthon) —valid name
militaris Horn 1870: 46 (Canthon)—jr. subj. syn. simplex LeConte [Robinson 1948: 87]
mixtus Robinson 1948: 91 (Canthon) —jr. subj. syn. puncticollis LeConte, new synonymy
nyctelius Bates 1887: 31 (Canthon) —jr. subj. syn. puncticollis LeConte [Schaeffer 1915: 50]
praticola LeConte 1859c: 10 (Canthon) —valid name
probus Germar 1823: 98 (Ateuchus) —valid name
puncticollis LeConte 1866: 381 (Canthon) —valid name
simplex LeConte 1857: 41 (Canthon) —valid name
vetustus Pierce 1946: 122 (Canthon)—jr. subj. syn. praticola LeConte [Robinson 1981: 626]
Key to the Species of Boreocanthon Halffter
Note. Boreocanthon comprises species that are often widely distributed and patently variable. The following key relies mostly upon generalizations about structure and, therefore, cannot be expected to accommodate inevitable exceptions. Reliability of identifications will be enhanced if target specimens are free or largely so of significant wear, especially to the head margin and to the dorsal surface. Since closely related Boreocanthon species are commonly allopatric, accurate locality information is an important corroborator of diagnostic structural features in this genus. The text page position for each species treatment is indicated in brackets following the species name.
1. Dorsal sculpturing (including the pygidium) consisting of coarse granulation on shagreen (alutaceous) background (Fig. 8, 13, 27); granules discrete, round, raised above surface, distinct punctures and shiny microspots lacking. Notch separating clypeus from paraocular area large, setting off tooth-like anterior angle of paraocular area such that head appears strongly sexdentate (Fig. 4, 11, 20)............... 2
— Dorsal sculpture variable but not including discrete, raised, rounded granules; pronotum either punctate on shagreen background, or (B. lecontei, Fig. 31) covered by dense, fine granulation largely supplanting shagreen background. Dorsum (Fig. 48, 75) usually presenting shiny microspots, especially on pronotum (except B. lecontei), elytra and often also on head and pygidium. Paraocular areas and dentition variable................................................................................ 4
2. Form of protibial spur same in both sexes, viz, strongly curved laterad and tapering to acute point (Fig. 20). Posterior portion of lateral pronotal margin asperate (serrate). Hypomeral carina absent (Fig. 24). Protibia (viewed along inner margin) abruptly widened (offset) at level of third (basal) tooth; inner apical angle produced as small, conical, apically-directed tooth (Fig. 16, arrow). Pygidium distinctly impressed basally, resulting transverse concavity often divided by median, longitudinal swelling (Fig. 14, 27). Compressed tip of parameres (viewed laterally) in form of elongate triangle (Fig. 18).................. 3
— Protibial spur sexually dimorphic: strongly curved laterad and tapering to acute point in female; nearly straight to curved laterad, apically slightly expanded and obliquely truncated or asymmetrically notched in male (as in Fig. 116a,b). Posterior portion of lateral pronotal margin smooth. Hypomeral carina present, sometimes only slightly developed. Protibia usually only gently sinuous at level of basal tooth. Pygidium evenly convex, not impressed basally (Fig. 6). Compressed tip of parameres short, truncated.
Length 5–10.5 mm. Very widely ranging from south central Canada to northern Mexican Plateau, extending westward into eastern Arizona (Fig. 10)....... Boreocanthon praticola (LeConte) [p. 13]
3. Pronotal granules uniform in size and shape, evenly and densely distributed and seldom coalescent (Fig. 11, 13b). Surface granulation extending to pteropleura but much weaker on median area of metaventrite and absent or only weakly evident on abdominal ventrites. Circumnotal ridge becoming very fine posteriorly, extending around posterior pronotal angle mesally to point adjacent to 7 th or 8 th elytral stria (Fig. 13b, arrows). Dorsum dark but almost always presenting metallic green coloration (viewed under bright light). Length 6–10 mm. Southeastern United States from Louisiana to North Carolina (Fig. 28)..................................................... Boreocanthon depressipennis (LeConte) [p. 18]
— Pronotal granules larger, variable sized and frequently coalescent, especially on disk (Fig. 13a, 19). Surface granulation extending to pteropleura, at least anterior portion of median area of metaventrite, and at least sides of all abdominal ventrites. Circumnotal ridge ending at posterior pronotal angle, not extending onto posterior pronotal margin (Fig. 13a). Black, only very rarely with any hint of color. Length 6–11 mm. United States west of Mississippi River to Rocky Mountains with southwestern extension through Texas to southeast Arizona (Fig. 28)........................... Boreocanthon ebenus (Say) [p. 20]
4. Pronotum very finely, densely granulate, granulation highly coalescent largely supplanting shagreen background; punctures absent (Fig. 29–31). Paraocular notch very small, sometimes almost obsolete, scarcely if at all breaching raised lateral margin of head (Fig. 29, 32). Smaller beetles, overall length not exceeding 5 mm. Southern Texas and northern Tamaulipas (Fig. 100)... Boreocanthon lecontei (Harold) [p. 26]
— Pronotum distinctly punctate, usually on distinctly shagreen background, punctures can be bold or very fine and widely dispersed such that pronotal surface appears almost smooth; pronotum never granulate. Paraocular notch variable................................................................. 5
5. Dorsum bright metallic green, often with yellow or coppery highlights (Fig. 36–39). Pronotum strongly but not densely punctate, shiny, shagreen background mostly effaced, sometimes detectable in isolated patches near anterior angles (Fig. 38). Upper surface of head strongly roughened by large, closely packed, coalesced punctures. Length 4.5–6.0 mm. Sierra Madre del Sur, Mexico (Fig. 45)........................................................................ Boreocanthon ateuchiceps (Bates) [p. 28]
— Dorsum dark, usually black, sometimes with blue or green highlights (producing dark, metallic green color in B. forreri). Pronotum punctate, often finely and sparsely so; shagreen background and shiny spots distinct, only rarely obscured. Upper surface of head smooth, with subtle punctures except anterior portion of clypeus, which is usually distinctly roughened. Length variable. Distribution north of Transverse Volcanic Range in Mexico northward to southern Canada ..................................... 6
6. Paraocular notch obsolete, anterior angle of paraocular area never accentuated (Fig. 47, 52). Clypeal margin usually bearing four perceptible teeth, median pair short, broadly rounded, wider at base than long, lateral two always small and inconspicuous and sometimes virtually absent such that clypeus appears bidentate (Fig. 46–47). Pronotum (viewed in profile) strongly raised above level of elytra (“humpbacked,” Fig. 53b). Protibia abruptly widened, inner margin offset at level of basal lateral tooth (Fig. 51). Larger sized, length 7–11 mm. Distribution restricted to northwestern flank of Sierra Madre Oriental in southwest Nuevo Leon /southeast Coahuila, Mexico (Fig. 101)................................................................................. B oreocanthon coahuilensis (Howden) [p. 31]
— Paraocular notch (in unworn specimens) evident, sometimes very small, more often excising head margin and setting off angular prominence of paraocular area; shape of head margin variable but always distinctly quadridentate or sexdentate. Pronotum (viewed in profile) most often evenly rounded and at most only slightly raised above level of elytra. Protibia only gradually widened toward apex, any offset only weakly indicated. Smaller, length generally less than 7 mm. Widely distributed in Mexico and the United States ............................................................................ 7
7. Lower apical angles of parameres expanded laterally as thin rounded or elongate flanges (Fig. 56–57, 68a). Margins of elytral striae 1–4 and sometimes also 5–6 sharply defined by carinulae extending from base at least one-third total length (Fig. 71). Paraocular notch deep, setting off strong, angulate portion of paraocular area, head appearing clearly sexdentate (Fig. 62, 66)................................ 8
— Lower apical angles of parameres in form of elongate, distally rounded swellings (Fig. 77, 86, 93), not flanged. Margins of elytral striae either not carinulate, or only briefly so anteriorly and then in occasional specimens showing metallic highlights. Paraocular notch variable.................................. 9
8. Ventral apical angle of parameres, viewed caudally, with ear-shaped, rounded or slightly angulate flanges (Fig. 56–57). Second and third elytral interstriae conspicuously swollen anteriorly, these raised areas flanking deeply impressed first interstriae (Fig. 59). Pronotum distinctly impressed posteromedially, resulting concavity almost smooth and contiguous with depression formed by first interstriae of elytra (Fig. 55). Epipleural (9 th) stria usually visible posteriorly. Mesoventrite at most with few central punctures. Dorsum, viewed in bright light under magnification, with strong, royal blue (very rarely green) undertone (intensified when surface is wet). Length 4.0– 6.5 mm. Baja California del Sur, the Mexican Plateau and adjacent areas of Arizona, New Mexico and western Texas (Fig. 63)...................................................................... Boreocanthon puncticollis (LeConte) [p. 33]
— Ventral apical angle of parameres, viewed caudally, in form of elongate flanges (Fig. 68). Second and third elytral interstriae usually not conspicuously swollen; pronotum lacking distinct posteromedian concavity. Epipleural (9 th) stria effaced. Mesoventrite completely coarsely punctured (Fig. 70). Dorsum black, lacking strong blue undertone. Length 4.0– 5.5 mm. Southern Texas and far northeast Mexico (Fig. 63)................................................. Boreocanthon integricollis (Schaeffer) [p. 38]
9. Paraocular notch large, lateral margin of paraocular area strongly salient (Fig. 72, 74). Clypeal teeth large, acute. United States east of the Rocky Mountains and central New Mexico ...................... 10
— Paraocular notch obscure, anterior angle of paraocular area interrupting curve of head margin as small, angulate corner (Fig. 92, 106, 112). Clypeal teeth obtuse, broadly rounded apically. Southeastern Arizona southward along coast of mainland Mexico to Nayarit ................................... 11
Note. Couplet 10 separates taxa for which intermediate populations exist in west Texas and eastern New Mexico. Some specimens from Ward and Winkler Counties in Texas, and Eddy and Lea Counties in New Mexico can be difficult to sort morphologically; they are here regarded as B. probus on the basis of distribution. See Comments for B. probus.
10. Pronotum not at all or only weakly (narrowly) explanate anterolaterally. Paraocular notch narrow, setting off strong, anteriorly directed tooth, head strongly sexdentate (Fig. 72, 74). Anterior portion of head behind clypeal teeth often abruptly shinier and rougher than posterior portion, which is smooth and punctate over shagreen background (Fig. 79). Subhumeral (8 th) stria simple or only weakly, if at all carinulate. Profile of compressed distal portion of parameres in form of equilateral triangular (Fig. 76). Length 4.0– 5.5 mm. Eastern United States from Atlantic coast to Rocky Mountains roughly south of 41 st parallel, Texas and New Mexico east of the Pecos River (Fig. 82)........... Boreocanthon probus (Germar) [p. 40]
— Pronotum widely explanate, upturned narrowly at lateral angle and progressively more widely so toward anterior angle (Fig. 84, 87). Paraocular notch setting off transverse anterior margin of paraocular area, head strongly quadridentate (Fig. 83, 89). Anterior portion of clypeus dull, only rarely weakly shinier than rest of head surface (Fig. 89). Subhumeral (8 th) elytral stria carinulate, usually sharply so from umbone to midpoint of elytral margin or slightly beyond (Fig. 88, arrow). Compressed distal portion of parameres, viewed laterally, in shape of elongate triangle (Fig. 85). Length 4.5–6.5 mm. Rio Grande drainage of New Mexico and Texas from Albuquerque southward to El Paso and Chihuahua (Fig. 82, inset)............................................. Boreocanthon halffteri, new species [p. 45]
11. Median clypeal teeth broadly rounded, lateral clypeal teeth small, length less than half that of median teeth; margin of head appearing quadridentate (Fig. 92). Pronotal puncturing usually only weakly indicated, only occasionally conspicuous (×10). Subhumeral (8 th) elytral stria never carinulate (Fig. 99); striae 7 and 8, sometimes also 6, often noticeably weaker than discal striae, anterior one-half or more of 7 th and 8 th sometimes nearly effaced. Compressed distal portion of parameres (viewed laterally) triangular (Fig. 94). Widely distributed in the western United States and Canada from the Rocky Mountains westward to Pacific coast, extending northward to southern British Columbia and southward to northwestern Baja California (Fig. 100–101).............................. Boreocanthon simplex (LeConte) [p. 48]
— Median clypeal teeth rounded or acute, lateral teeth prominent, length at least one-half that of median teeth, margin of head hardly sexdentate (Fig. 106, 112). Pronotal puncturing always conspicuous (×10; Fig. 105). Subhumeral (8 th) elytral stria always at least finely carinulate (Fig. 107, 115); elytral striae usually uniform, although base of 7 th usually effaced at elytral umbone. Compressed distal portion of parameres (viewed laterally, Fig. 113) very short, truncate (“snub nosed”). Southern Arizona and west coast of mainland Mexico ....................................................................... 12
12. Dorsum dark metallic green or yellow-green, rarely black; venter with green reflections on legs and pleura (Fig. 102–103, 107). Anterior ends of 2 nd and 3 rd elytral interstriae not swollen or only very weakly so (Fig. 102–103). Western coast of mainland Mexico from far southern Sonora to Nayarit (Fig. 45).............................................................. Boreocanthon forreri (Bates) [p. 56]
— Dorsum and venter black, often with green or blue sheen (intensified when surface is wet). Anterior ends of 2 nd and 3 rd elytral interstriae distinctly swollen (Fig. 110–111). South-central Arizona southward into northwestern Sonora (Fig. 45)......................... Boreocanthon melanus (Robinson) [p. 58]
description: Published as part of Edmonds, W. D., 2022, Taxonomic review of the North American dung beetle genus Boreocanthon Halffter, 1958 (Coleoptera: Scarabaeidae: Scarabaeinae: Deltochilini), pp. 1-65 in Insecta Mundi 2022 (952) on pages 7-13, DOI: 10.5281/zenodo.7399212