206 BULLETIN 63, UNITED STATES NATIONAL MUSEUM. 



The elytra at base are not margined nor adapted to receive the pro- 

 thoracic base, as is the case in the majority of species of the Dentipes 

 group; on the other hand the elytral base declines, corresponding 

 exactly in structure Avith ohscura. 



In either group it would prove a disturbing element and the only 

 course to pursue in the search for taxonomical harmony is to place 

 it in a group as here indicated. It is also very evident that it is a dis- 

 tinct species, which has undergone practically no differentiation into 

 distinct races — in this it is analogous to veterator — although it is 

 slowly yielding to the modifying influences of environment. 



It probably represents a very slightly changed branch of the com- 

 mon ancestral stem from which the earlier antecedents of the present 

 Obscura and Dentipes groujDS took their origin. In a genealogical 

 scheme it must be placed to show the greatest affinity for dispersa. 

 Divergent elements can not be arranged in a linear series of mor- 

 phological or specific sequence. 



The form of the prothorax is not so very different from that ob- 

 served in ohscura. 



The tibial spurs are broader and larger than is seen in the Dentipes 

 group, and resemble those of ohseiiiHi. In the male the spurs are of 

 the same form, but smaller, shorter, and narrower; in the female the 

 protibial spurs are more strongly divergent than in dentipes., and less 

 so than in ohscura. 



It remains for a critical research into the faunal congeneric con- 

 stituents of Mexico to further elucidate the relationships of this in- 

 teresting species. 



The group genital characters are as follows: 



Male. — Apicale of the edeagophore elongately triangular; surface 

 convex and not grooved ; sides nearly straight ; base with an obtuse 

 lobe at middle and feebly sinuate laterally. Sternite slightly trans- 

 verse, each lobe broadly rounded at tip, not separated at base by a 

 distinctly oval membranous area, and the membrane is not setose 

 across the base of the sinus. 



Female. — Genital segment triangulo-trapezoidal. Valinda: Dorsal 

 plate oblong, surface broadly concave, more deeply so internally, in- 

 ternal border strongly reflexed, externally not at all retracted ; apical 

 margin truncate. Apex short and triangular. 



Apj)enda(/e conical and truncate. Superior pudendal membrane 

 not reaching beyond the middle of the dorsal plate and longitudinally 

 rugulose. Submarginal groove feeble and not visible from above. 



The genital characters show greater affinity with the Denti])es 

 group; the external characters show greater resemblance to the Ob- 

 scura group. 



It is undoubtedly intermediate. Compare Plate 1, figs. 8, 15, and 

 16; Plate 3, figs. 12 and 13. 



