1883.] NATURAL SCIENCES OF PHILADELPHIA, 175 



summer. Where known, I give the name of the collector as 

 authority for localit}'. (1) From dredgings of P^-ramid Lake 

 bottom; Bussell (I. C); August 30, 1882. (2) North side of 

 P^-raraid Lake, Nevada; BusseU (I. C). (3) In tufa, shore of 

 Walker's Lake, Nevada ; Bussell (I. C), and also loose. This is 

 the locality represented by the shells sent to you. 



" P^-ramid Lake,' although it receives the fresh water of the 

 Truckee River, the outlet of that gem of lakes, Tahoe, is very 

 strongly alkaline, and the water is not good for human use, 

 although it can be used for a short period without much incon- 

 venience." 



The elevation of Pyramid Lake is 4890 feet, as stated in 

 Gannett's'^ List, etc., and Walker's Lake, according to the same 

 authority, has an altitude of 8840 feet. The water of this lake 

 is probably similar to that of Pyramid ; it is brackish, as I have 

 been informed by Prof. Joseph LeConte. 



These lakes are the remnants of the great tertiary lake which 

 covered this general region, and are the pockets or deeper 

 depressions in the floor of the ancient lake ; the bitterness of 

 their waters being the result of the accumulated alkaline and 

 saline sediments, or dregs, of centuries. 



Assuming that I have placed the above form in its proper 

 position, much greater interest attaches to it than that of the 

 addition of a new species to the fauna of the general region 

 within which it is found, or that of adding a peculiar t3'pe to the 

 living molluscan fauna of the North American continent. 



The species of Pyrcjula heretofore described,^ are the type, P. 

 helvetica, from Switzerland; P. bicarinata, France; P.pyrenaica, 

 from the Pyrenees ; and P. andicola, from the Andes of Bolivia. 



Its- distribution hitherto, it will be seen, is Europe and South 

 America ; inhabiting, as Stimpson observed, " fresh waters in 

 mountainous regions," and as he further remarked, " It is inter- 

 es^ting to notice that all the species of the genus as yet described 

 are severally reported to occur in mountainous districts ; an 

 instance of correlation of form to external conditions," 



' Lieut. Symons, in Lieut. Wheeler's Report Geog. Survey, etc., 1878, 

 p. 114. 



•^ U. S. Geol. Survey. Hayden, Misc. Pub., No. 1. Fourth Ed. 



^ Vide Stimpson, ihid. 



