THE NAUTILUS. 



Vor,. XVI. FEBRUARY, 19O3. No. 10. 



NOTES ON PYRAMIDULA ELRODI PILS. 



BY MORTON J. ELROD. 



This shell was first collected on the sides of the Mission Mountains, 

 above Post Lake, in the summer of 1899. About forty were taken, 

 all dead. Specimens were sent to Dr. Pilsbry, of the Philadelphia 

 Academy of Sciences, who described the species in NAUTILUS, Vol. 

 XIV, 40, naming the shell after the collector. 



During the collecting expedition of the University of Montana 

 Biological Station, in July, 1900, a stay of ten days was made at 

 McDonald Lake for the express purpose of making further investiga- 

 tions of this species. During this time some three quarts of speci- 

 mens were collected, of all sizes and varying colors, from the dark 

 brown of the living shells to the bleached white of the dead ones. 

 Also some three dozen living snails were secured, which were 

 drowned, and in a number of cases, beautifully expanded. 



The distribution of the species, so far as known, appears to be quite 

 local, and is deserving of further study. At present it seems con- 

 fined to the mountain slopes forming the amphitheatre around and to 

 the east of Post Lake. On the south side of the lake, owing to the 

 dry ness of the rocks and soil, it appears very scarce, one living and 

 several dead shells being the result of an afternoon's search. A search 

 on the north bank during the same time on the same day resulted in 

 a quart of shells, a dozen living. While no search has been made in 

 the mountain slopes east of the lake, there can be little doubt of its 

 presence, since the shell is found on both sides of the lake. 



On the north slope of the lake four small streams tumble over the 



