6 MEMOIRS ON THE COLEOPTERA 



subbasal carina so distinct in that subspecies, smaller elytral punc- 

 tures, which are in no part serial in arrangement, and in the rather 

 elevated suture. From baroni Rivers, the type of which was taken 

 on the Gila River, it differs in its much more elongate form, more 

 elongate and less posteriorly narrowed elytra, the punctures of 

 which are very much smaller, and in the more oblique sides of the 

 prothorax. It differs from piccolominii Reiche, according to the 

 description, in its much smaller size, more slender form, alutaceous 

 surface and absence of coarse elytral punctures and of the inner 

 carinules. Longipes also differs from piccolominii in its smaller 

 size and opaque surface, but seems to resemble it in the coarse 

 elytral punctures and the three inwardly decreasing carinae. These 

 three species, or possibly in part subspecies, constitute the second 

 subgeneric group of Amblycheila. Schwarzi W. Horn, belongs to the 

 cylindriformis section of the genus, as also does piccolominii Rche. 



Omus Esch. 



There are some facts relating to Omus that remind us of Brennus. 

 Both genera are very abundantly represented in, and confined to, 

 the true Pacific coast fauna; both are nocturnal in habits and almost 

 uniformly deep black in color. Both are comparatively recent 

 geologically, which accounts for the local segregation of the numer- 

 ous individuals into more or less slightly differentiated taxonomic 

 elements. Some of these local developments have become specific 

 in status, others must be viewed as having less value at present. 

 Many of the latter category are doomed to early extinction, while 

 others, thus still more isolated, will progress to the role of distinct 

 species in conformity with the past history of these genera. It is 

 singular, it may be said in passing, how large a proportion of the 

 Coleoptera of the Pacific regions are black; even the few Scarabae- 

 idse are mostly black; the great Eleodes, Coniontis and Blapstinus 

 cohorts are of course black, as well as the larger part of the Cara- 

 bidae. This lugubrious nature of the fauna is due to nocturnal or 

 secluded habits, rendered necessary by peculiarities of climate, the 

 hot dry dusty days of the long summer not being well fitted to 

 support light loving and generally more highly colored types, in 

 spite of the bright sunshine, while the fogs and coolness of the night 

 result in adequate amounts of moisture. 



