ART. L'S REVISION" OF DISOISTYCHA NORTH OP MEXICO BLAKE 5 



They are smooth, except in the costate species, usually shining and 

 glabrous. The prosternum divides the coxae, and the precoxal cavi- 

 ties are open behind. The last visible sternite in the male is truncate 

 and in the female angulate. The legs are relatively short and the 

 tibiae feeblj^ sulcate on the outer edge with a short apical spur. In 

 the male the first joint of the anterior tarsi is much enlarged. The 

 claws have a short basal to,oth. 



The shape of the aedeagus corroborates the other structural char- 

 acters by which the species are separable into groups. In the 

 vittate species the shape of the aedeagus is of much greater value 

 in distinguishing relationships than is the coloration. The aedeagi 

 of the species with blue or green elytra are quite unlike those of any 

 of the vittate species except D. maritima., a species structurally 

 unique among the vittate ones. The aedeagi of these dark species 

 offer excellent specific differences. The aedeagus of D. funerea also 

 is quite unlike that of any other species. It is so difficult to describe 

 the shape of this structure that little has been attempted in the text, 

 but figures showing the dorsal, ventral, and lateral views have been 

 made and should be consulted in determining the species. 



The coloring is fairl}^ constant within a species. In the vittate 

 yellow and black species, the head maj' be pale, bicolored, or entirely 

 dark. The pronotum of the vittate species usually has at least 

 traces of 2 to 5 spots, which sometimes coalesce or band together. 

 The elytra usually have dark sutural, median, and submarginal or 

 marginal vittae. In some groups, as the discoidea group, the sub- 

 marginal vitta is either very faint or lacking. The median and 

 sutural vittae are usually present except in pale varieties of a species, 

 in which they may become interrupted or disappear. Only 1 or 2 

 pale species north of Mexico are without elytral vittae — antennata^ 

 an entirely pale Mexican species occurring only at the tip of Florida, 

 and -figurata^ also a Mexican species, found in this country in Arizona 

 and Nevada, in which the vittae are frequently indistinct. The spe- 

 cies having blue or green elytra are nearly as homogeneous in colora- 

 tion as the vittate species. The former can be distinguished from 

 one another by the color of the head, femora, and lower surface, 

 which ma}^ be pale, bicolored, or dark. Only one, funerea^ is entirely 

 dark except for the last ventral segment, and this species is struc- 

 turally unlike the others. 



DESCRIPTION OF THE GROUPS 



Since 10 of the 32 species found in the United States do not fall 

 into any natural group known to me, and since 3 of the others are 

 the only representatives of 2 southern groups, I have not been able 

 to work out a satisfactory natural key according to these groups. 

 In lieu of this, a short discussion of the groups is here given, with 



