Z CALIFORNIA ACADEMY OF SCIENCES. 



these ravines, where they exist in enormous profusion, not 

 oul}^ individually, but in species indiscriminately mingled; 

 such for instance Avas a small area of precipitous rocks cov- 

 ered with mould, moss and thin grass, in the deep ravine at 

 Gilroy Springs, Santa Clara County, where a small trickling 

 stream f i-om one of the sulphurous soda-springs enters the 

 creek below. Here I obtained hundreds of specimens of 

 seven distinct species; associated with them were an equal 

 multitude of Steni represented by several species. This 

 concentration of insect life, which is one of the peculiarities 

 of faunal distribution in the Pacific regions, is to be 

 accounted for in a measure by the nature of the climate, 

 the long hot summers drying and baking the surface of the 

 ground, and driving all species, except the comparatively 

 few especially constituted to Avithstand such conditions, to 

 the moist and secluded localities above mentioned. 



The study and in'oper classification of these varied forms 

 is a matter of considerable, although by no means of insu- 

 perable difficulty, tliere being one important characteristic, 

 which is of very great aid to the investigator; this is the 

 facility with which they may be resolved into ijerfectly defi- 

 nite, and so far as the material collected will allow of judg- 

 ment — abruptly limited generic subdivisions. The principal 

 difficulty, therefore, consists in the proper ditlerentiation of 

 the species composing these groups, and which are often 

 very closely allied; but even here the difiiculty is partially 

 BU]ierficial, as when these closely allied forms are separated 

 and carefully studied, the}" are found to possess very little 

 variability, and tlie individuals of the several species ajij^ear 

 to be unusually uniform throughout extended series. 



The genera here considennl ]iossess certain characters 

 in common, among Avhicli may be mentioned the rather slen- 

 der nuixilhuy pal])i with the third joint very moderately 

 swollen and the fourth minute, subulate and oblique, but 

 distinctly visible; the antenna; also are singularly uniform 

 in structure throughout, being slender — or very slightly ro- 



