Diplocheila (Isorembus) major major (Le Conte 1847)

Diplocheila major major Le Conte
Rambus major Le Conte, 1848:418; [type specimen a female, in the Le Conte
coll., MCZ no. 5704]. Type locality: "ad urbes Detroit et Nov. Aureli-
amim"; (determined from original description). — Ibid., 1853:388. Diplochila major Horn, 1880:52. Wickham, 1896: 43.— Casey, 1913:148. Diplochila expansa Casey, ibid. ; [type specimen a female, in the Casey Coll.,
USNM no. 47372]. Type locality: Keokuk, Iowa; (determined from
original description). Rcmbus expansa Leng, 1918 : 62. Diplochila oblonga Casey, 1913:48; [type specimen a male, in the Casey Coll.,
USNM no. 47374]. Type locality: "Kansas"; (determined from original
description). Rembus oblonga Leng, 1918:63. Diplocheila procera Casey, 1920 : 200 ; [type specimen a female in Casey Coll.,
USNM no. 47373]. Type locality: "Lake Superior"; (determined from
original description).
The shallower emargination of the anterior margin of the pronotum, the marked rotundity of the sides in front of the widest point, and the presence of punctures in the deeper striae of the elytra distinguish this subspecies from the following one. In addition, there are mean differences between the two in the number of spines in the posterior median row of the hind tibiae (table 19).
Description. — Type, female. Labelled with a yellow disc (western states).
Length 18.3 mm., width 8.3 mm. Surface with a glossy luster. Sculpture as described for striato punctata group.
Frontal impressions at head linear, moderately deep, extending back a short distance beyond anterior margin of eyes. Eyes of average convexity.
Pronotum with anterior margin rather shallowly concave, slightly arcuate, not appearing strongly constricted in front of widest point, but rotund, slightlty constricted posteriorly ; impressions of dorsal surface shallow, posterior lateral impressions broad and shallow, linear pit at inner margin of impression short (fig. 44).
Elytra with striae 1-5 punctate, moderately deep and distinct, 6 shallower, 7 faintly indicated ; intervals moderately convex, right elytron with one puncture in interval 3, left with two punctures.
Retractile stylus not studied.
Variation. — Data on variation in length, width, and number of spines in the posterior median row of the hind tibiae are presented in tables 17-19. Frontal impressions of the head vary in extent and depth. The pronotum is more or less trapezoidal in shape. The sides are somewhat arcuate, generally rotund anteriorly, little constricted basally, the sides sinuate posteriorly in some individuals. The surface impressions are about the same as in the type.
The elytral intervals vary from broadly and strongly convex to weakly convex. Striae 1-5 are in most individuals the same as in the type, however, in a few, 5 is less pronounced than 1-4. Striae 6 is always finer than 1-4 and 7 varies from weakly developed to absent.
Retractile stylus of the female and genitalia of the male as in striatopunctata (3 males and 3 females dissected).
Type Locality. — Although two localities are given by Le Conte in his description of Diplocheila major, Detroit and New Orleans, the locality from which the type came is not clear. The specimen labelled as type in the Le Conte Collection is not a member of the Gulf Coast population and the original description does not fit Gulf Coastal specimens of this species. As the only " New Orleans " in the United States is on the Gulf Coast, it seems reasonable to assume that this is not the type locality, thus leaving " Detroit " for consideration. The type specimen of major is labelled with a yellow disc signifying that this specimen was collected in the " western states ". The only " Detroit " occurring in Le Conte's " western states ", of which I am aware, is in northeastern Texas. My opinion is that Detroit, Texas is the type locality of D. m. major.
Synonymical Notes. — Three synonyms of this subspecies were described by Casey who applied the name major Le Conte to a Louisiana specimen in his collection, and thus to the Gulf Coast population. Diplocheila oblong a and proccra were differentiated from and described in terms of D. expansa. Therefore, I will first give reasons for regarding major major Le Conte and expansa Casey as conspecific, and then discuss the other two named forms in terms of the type specimen of expansa.
The pronotum of the type specimen of expansa is about the same in shape as that of the type of major, and the two specimens are of about the same size {expansa is .9 mm. longer and .5 mm. wider than major). The principal difference is that elytral stria 7 is completely lacking in expansa, whereas in major it is weakly indicated. However, this character is variable.
D. oblonga was based on a series of three males, all of which fall within the range of size variation for D. major: total length — 16.7-19.9 mm. ; maximum width : 8.2-8.4 mm. Elytral stria 7 is faintly indicated and 6 is somewhat weaker than usual. However, the relative distinctness of stria 7 is too variable to be of much value taxonomically within the species major. The general body form is described as being narrower than in expansa. If this is true oblonga should have higher values for the ratio total length/maximum width. The range of variation for this ratio in the type series of expansa is 2.16-2.17, and in the type series of oblonga it is 1.97-2.28. The type specimen of oblonga, with a ratio of 2.28, is actually narrower than the type specimen of expansa with a ratio of 2.17. However, the two paratypes of oblonga are proportionately broader than the type and paratype of expanse The pronotum is somewhat more strongly sinuate posteriorly in oblonga than in expansa, but this feature also varies sufficiently as to be characteristic of individuals rather than population samples. Elytral punctation varies in the type series from fine to coarse, the expected range in the northern subspecies of major. The type specimens of oblonga and expansa can be distinguished from one another but the gaps between them are bridged by the characters of other individuals, so the two are conspecific.
D. procera Casey was described from a single female (length 18.4 mm., width 8.4 mm.). This form differs from expansa by the form of the frontal impressions, a character which is highly variable in Diplocheila major. The body form is supposed to be much narrower, but the value for the ratio total L/max. W is 2.19 for procera and 2.16 for expansa. This slight difference does not seem worthy of taxonomic recognition. The pronotum is supposed to be less transverse {expansa PN: W/L 1.57, procera PN : W/L 1.42, type of major LeC. PN : W/L 1.58) but the calculated range of variation of major includes all three of these values (Ball 1954: 222-223).