ART. 2 REVISION OF TRIRHABDA NORTH OF MEXICO BLAKE 5 



the outer sides are darkened. The principal leg characters differ- 

 entiating Trirhdbda as a genus are (1) the first tarsal joint longer 

 than the following joints, (2) the absence of a well-marked external 

 sulcus in the tibia, and (3) the bifid claws. 



The size and shape of the aedeagus furnish good specific charac- 

 ters, which may well be used also to indicate generic boundaries. 

 As it is extremely difficult to interpret descriptions of the shape of 

 the aedeagus, I have in all species made a drawing of the dorsal 

 view showing the shape of the tip, which varies greatly in length 

 and shape — in some it is short and blunt, in others long and taper- 

 ing; in some pointed, in others rounded; but in all the species the 

 aedeagus is long and narrow and with a more or less acute, never 

 truncate tip. In the convergens group the aedeagus varies but 

 little. It may be that the whole group is a single species that has 

 become separated into races in its wide geographic range, and these 

 races have become quite different in coloring and markings. I am 

 unable to inflate the internal sac of the aedeagus and do not know 

 if even that would be of value in determining the species. In the 

 luteocincta group the aedeagus is peculiar in its long tapering tip. 

 Under luteocincta have been grouped two other species whose differ- 

 ences no one had suspected, but dissection revealed aedeagi so unlike 

 that I at once began to hunt for and find external characters. The 

 same was true of canadensis and adela, attenuata and pilosa, virgata 

 and horealis. 



The quite different structure of the aedeagus of T. hrevicoUis first 

 led me to suspect that it might belong to a different genus. Later 

 the dissection of a Mexican Monocesta brought to light the same sort 

 of aedeagus. This Monocesta is closely related to if not identical 

 with Schaeffer's Trirhabda ornata^ of which I have seen only a 

 single specimen, the type. T. ornata without doubt would have a 

 similar aedeagus. Besides having a different aedeagus from Tri- 

 rhabda^ these three species have a differently shaped prothorax and 

 are further distinguished by minor details of coloring and pubes- 

 cence, and are herein described (p. 32) as a new genus. In addi- 

 tion to figures of the aedeagi of all the species of Trirhabda^ I have 

 given drawings of those of one or more species of each of the three 

 closely allied genera, species of which have been ascribed to 

 Trirhabda. 



EGGS AND LARVAL HABITS 



The life history of one of the most widespread species of TH- 

 rhabda, T. canadensis^ an account of which by W. V. Balduf has been 

 published,^ is probably typical of the genus. The eggs, laid on the 

 ground, are in clusters glued together bj'^ some strong adhesive and 



"Ent. News, vol. 40, no. 2, pp. 35-39, 1929. 



