Mar. 1899.] Fall: On American Species of Acma:odeka. 3 



Notwithstanding tliat the form of the prosternuni is thus in some 

 measure unsatisfactory as a point of departure, a better has yet to be 

 found and I shall continue the division into groups substantially as 

 proposed by Horn, calling attention in the proper place to the am- 

 biguous forms. 



That modification of the last ventral segment variouslv described 

 as the apical ridge, plate, crest or carina, is certainly of exceptional 

 value in specific characterization. It may be thick or thin, broadly or 

 narrowly rounded, truncate or angulate, with regular or irregular edge, 

 but I have never in the hundreds of specimens examined discovered 

 any variation in type within specific limits. It does vary somewhat 

 in development in certain species and very rarely to such a degree as 

 to be either well developed or quite lacking in the same species. 

 This fact together with its apparent lack of coordination with other 

 features of structure or facies, render it unfit for a means of primary 

 division, though it was thus made use of by Leconte for the sixteen 

 species treated in his revision of 1859. 



Further experience shows that the yellow spot at the side of the 

 thorax is much less constant than was supposed by Horn, there being 

 at least nine species in which it may be either. present or absent. Ex- 

 ternal sexual characters seem to be almost lacking. The last ventral 

 segment in the males of certain species has been observed to be shorter 

 and more truncate at tip than in the female, but the difference is feeble 

 and I have not attempted to investigate the extent or constancy of its 

 occurrence. In certain small species of the Truncate {tubiihis and 

 allies) the claws in the males are provided with a distinctly longer, 

 stouter tooth than in the females. I have not noticed a similar dis- 

 parity elsewhere, but I am not prepared to say that it does not exist. 

 The character has not been used at all in classification, and the student 

 who has a sufficient series of specimens can, if he is curious, easily in- 

 vestigate for himself. 



In distribution the genus is practically confined to the southwestern 

 region. Aside from the two West Indian species — cubcEcola and pul- 

 cherrivia, which have lately been found on the Florida Keys, three 

 species only — ornata, pulchella and culta — are known from the region 

 east of the Mississippi River ; variegata extends its range into eastern 

 Oregon ; all other species hail from the territory embraced by the fol- 

 lowing States or Territories — Texas, New Mexico, Colorado, Utah, 

 Arizona, Nevada and the Californias. At the time of Horn's revision 



