ART. 2 REVISION" OF TEIRHABDA NOETH OF MEXICO BLAKE 7 



part of the United States and southern Canada, canadensis reaching 

 the Pacific coast, although vlrgata is not found beyond the Great 

 Plains. 



A small group of three boreal species, the convergens group, all 

 occurring on goldenrod, is found (1) in Nova Scotia, (2) along 

 the shores of Lake Superior in Ontario and Wisconsin, to Manitoba 

 and Alberta, and (3) in Alberta and in the Rocky Blount ains south- 

 ward to New Mexico, These species are all closely related and may 

 be merely geographic varieties of one northern species. They are 

 all small (the smallest of the genus) and similar in sculj^ture and 

 pubescence, all have darkened ventral surface and heavy occipital 

 and pronotal markings, and all have similar aedeagi. They differ 

 chiefl}^ in elytral coloring and present little intergradation in their 

 separate localities. The Nova Scotia species is as readily separable 

 from the Lake Superior species as both are from the Alberta and 

 Rocky IVIountain species. Moreover, the Lake Superior species 

 has been found in Alberta preserving its distinctive coloration. Be- 

 cause they are so readily separated, I have given names to each 

 form, although structurally there is little to distinguish them. 

 Another northern species, horealis, extends from Massachusetts 

 through Michigan and the Dakotas to Montana and Washington, 

 but is recorded south of these States only from West Virginia, where 

 it probably was found in the mountains, and from Kansas and 

 Missouri. Four species are almost confined to the area from the 

 Great Plains west through the Rocky Mountains. T. leioisii is re- 

 stricted to the Rocky Mountain region and lives on Ghrysothamnus. 

 T. nitidicoUis, also found on Ghrysothamnus^ occurs from Wyoming 

 to Arizona and New Mexico and into the arid southern part of Cali- 

 fornia. It presents many color variations, although the pattern of 

 the markings is quite uniform throughout its range. T. attenuata 

 feeds on both goldenrod and sagebrush, and has a range from the 

 Great Plains (Kansas and Nebraska) to Alberta and through the 

 northern Rocky Mountain region in the United States. T. filosa 

 extends from Wyoming and Nevada into the Sierra Nevada in 

 California. 



On the Pacific coast the species of Trirhahda are manifold, with 

 extremely variable markings, and present most interesting relation- 

 ships. T. luteocincta occurs on the southern coast of California on 

 a species of Aplopappus, and T. labrata^ its close relative, is found 

 about Monterey on Aplopajjpus erlcoides. Another closely related 

 species, confusa^ said to be a sagebrush feeder, is found chiefly in- 

 land, and still another, sericotrachyla, which has hitherto been con- 

 fused with hiteocincta^ appears to be found only along the coast from 

 San Diego to Los Angeles. T. -fiavolinibata^ which feeds on Bac- 

 chaHs pilularis^ has been collected only in the San Francisco region. 



