Nevada Dytiscidae (Coleoptera)

Abstract

Extensive collecting during the past decade has indicated that Nevada, without doubt the most arid of the 48 states, has a comparatively large and varied aquatic coleopterous fauna. Of the total state area of 70,841,600 acres (_ 110,690 square miles), only 556,160 acres (869 square miles) were listed as water surface by the Nevada Surveyor-General's office in 1913. Disregarding the inaccuracies of these figures,2 they are, by virtue of climatic vicissitudes, merely approximations since many lake surfaces entirely disappear in dry years, most of the major rivers are subject to torrential flows of short duration, and may even dry up in the lower portions of their courses during late summer, and a great many smaller streams are entirely annual, appearing in late winter early spring, and drying completely during summer and fall. In addition, deflection of flow for irrigation projects has aided in eliminating some water surfaces then (1913) in existence, such as the recently dried Winnemucca lake which only a few years ago was a body of water nearly 30 miles long. This represents a loss of approximately 15% of the state water surface.2 However, the above figures suffice to point out the small proportion of water-to-land surface in the state, although in the matter of lakes, Nevada appears more favored than such neighboring states as Arizona, which have no natural standing water bodies comparable to Pyramid and Walker Lakes. The small water surface in Nevada can be attributed to the low general precipitation of the region, brought about largely by the idiosyncracies of Great Basin topography. The immediate restrictive consequences of the westerly Sierra Nevada range are forcefully reflected in the pronounced rainshadow effects along the eastern face of the range. These are strong enough to be felt for a considerable distance eastward, and are primarily responsible for producing a distinctive biologic route, which I have called the Sonoran Trailway,