1904 ENTOMOLOGICAL SOCIETY. 45 



Eleodes, circus bugs as they are called in the West ; and a considerable num- 

 ber of the genus Bemhidium, ground beetles that pick up a living on the 

 shores of streams and pools, not dwelling at any considerable distance from 

 moisture. Many others might be named, but I have endeavored to call at- 

 tfntion only to a few of the more striking instances. 



In studying the shore-inhabiting species just mentioned, the question has 

 arisen, whence do they owe their origin ? Are they immigrants from the sur- 

 rounding lands, and if so, do they come from the north or south, the east or 

 west? Do they have near allies on the shores of lakes lying outside of the 

 Great Basin, or are they isolated types that may be supposed to have arisen 

 *ti\ the ground thej'' now occupy? My own belief, founded on several years' 

 work with material collected on my trips to nearly every part of the Great 

 Basin and the surrounding districts, is that they are true endemics — that 

 tl ey have undoubtedly arisen, as species, in their present locations or the im- 

 mediate vicinity thereof. Occasionally a small colony may be established 

 in the outlying districts adjacent to the Basin, but such cases are rare. A 

 study of the distribution of some of the principal types, will, in my mind, 

 cast a good deal of light on the question as to whether or not these beetles 

 are recent acquisitions to the Basin fauna. It is unnecessary to enter into 

 details here, as I have gone over the matter with more minuteness in a paper 

 now in press. 



Taking as an example, one of the tiger beetles, Cicindela echo Casey, we 

 iind it distributed as follows, — on the mud beaches of Great Salt Lake, Utah 

 Lake, Sevier Lake and Little Salt Lake, in Utah; at Humbolt Lake, in Ne- 

 vada; and at Honey Lake in eastern California. All these points lie within 

 the Great Basin, and the beetle is entirely unknown from any other localities, 

 though it has a close relative, Cicindela pseudosenilis, at Owens' Lake, also 

 within the Basin. All these lakes are now separated by miles of burning 

 desert, forming a barrier that completely prohibits intercourse between the 

 different colonies. The breeding of the species on these deserts is equally im- 

 possible, since a certain amount of moisture, the year round, is necessary for 

 its growth. 



How are we to explain such a distribution? Why do we tind colonies, 

 (- idently arising from the same stock, though the members of one differ more 

 <.r less from those of another, scattered in these widely separated localities, 

 when it is perfectly evident that conditions are such that passage from one 

 lake to another is out of the question? My reply is, we must look to the an- 

 cient history of the region — to its geological record — for our answer. 



Even the earliest explorers of the Great Basin noticed that the terraces 

 on the mountains near Great Salt Lake indicated the former existence of a 

 much larger body of water on the same site. The geologists of the United 

 States Geological Survey have completed a study of the evidence, and have 

 mapped the boundaries of the great lakes that are now known to have occu- 

 pied the valleys during the Pleistocene periods. Their maps show the exist- 

 ence of two principal water bodies, one to the eastward, which has received 

 the name Lake Bonneville, and one to the westward, known as Lake Lahon- 

 tan. Between them was a plateau, dotted with smaller lakes. 



With the passage of the ages, there came about a great diminution of 

 the rainfall, and a consequent shrinkage of the great lakes of the Basin. 

 Then came a period of humidity and a second rise of the waters, followed by 

 « time of drought even more complete. The lakes, as a result, lost greatly in 

 Volume, bays became detached from the main bodies, forming separate inde- 

 pendent lakes, each in its own restricted basin. Some of these, in their turn, 

 dried up altogether, others persisted,- though often, perhaps, only as small 



