8 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 79 



Among the arid-region forms is eriodictyonis, known chiefly from 

 the Mojave Desert region and found on a species of Eriodictyon 

 (Hydrophyllaceae). One other California species, diducta, also 

 feeds on Eriodictyon^ but occurs as far north as San Francisco. 

 These two species breeding on Eriodictyon are so closely related 

 that one is almost tempted to call them varieties of the same species. 

 T. diducta ranges southward and inland to Nevada, and specimens 

 from around Fresno are difficult to separate in general appearance 

 from eHodictyonis. Another very distinct species, caduca^ described 

 by Horn, has not been found outside Owens Valley. Two other 

 species, geminata and nigrohumeralis^ with the pale-brown coloring 

 typical of forms from arid regions, occur in New Mexico and Ari- 

 zona, and geminata extends to the Pacific coast through southern 

 California, but specimens collected there usually have much darker, 

 almost piceous, elytra. 



T. hrevicollis^ not a true Trirhahda^ feeds on prickly-ash 

 {Zanthoxylum) and occasionally is a pest on orange, both belong- 

 ing to the Rutaceae. It is found in the Gulf States and north in the 

 Middle States even to IMichigan. T. ornata^ also referred to the same 

 genus, is found only in Texas, and T. { = Goraia) suhcyanescens has 

 been recorded only from the southern tip of Texas in Cameron 

 and Hidalgo Counties. 



Without a fully representative collection, it is extremely difficult 

 to identify specimens of Trirhabda. The genus is homogeneous, 

 possessing few structural characters by which to separate the species ; 

 the species are with few exceptions variable in elytral markings and 

 coloring, and as a rule they can not be determined by their food 

 plant, since the majority feed on goldenrod or sagebrush or both. 

 The key here given will probably not prove satisfactory to those who 

 are not somewhat familiar with the group. In species that are 

 similar in external appearance, the shape of the aedeagi is of great 

 help in the identification. 



In designating paratypes of the new species, I have taken care to 

 list only other specimens bearing the same data as the type, although 

 in all cases a larger number of specimens of the species was at hand. 

 This is not generally the practice in entomology at present, but in 

 the case of a genus in which the species are so closely related and so 

 easily confused, it is desirable that the paratypes should be as nearly 

 as possible equivalent to the type. 



I have been fortunate in having many collections placed at my 

 disposal, and wish to thank the following men for their kindness 

 in sending me their own collections or those in their care: Nathan 

 Banks and P. J. Darlington, of the Museum of Comparative Zoology, 

 Cambridge, Mass. ; C. W. Johnson, of the Boston Society of Natural 



