SUBALPINE MOLLUSCA. 87 



and we must suppose he had not compared it with P. 

 glabratus. 



In the Proc. Cal. Acad. Sciences, Vol. IV, 1870, p. 

 100, I followed Binney's Land and Fresh-Water Shells 

 in giving stibcrenatus as a good species, but stated that 

 "specimens common inland closely resemble P. glabra- 

 tus,'' giving the distinctions between them. I still think 

 there are sufficient of these to retain the Western form, 

 as a subspecies at least, larger and rougher, with more 

 cylindrical whorls. If, as Ingersoll states, P. glabratus 

 is a reversed shell, the difference is still greater. But 

 Say's description only calls it sinistral, just as he did ev- 

 ery other Planorbis he described, except P. cor-piilentiis, 

 and the latter, if any, would be a reversed shell. The 

 similarity of the sides in glabratus would allow of either 

 conclusion, but the form of mouth in Binney's figure 

 seems like that of other dextral species. 



P. HORNii Tryon. In an article by Mr. H. P. Carlton, 

 published also in Vol. IV of our Proceedings, this name 

 is given to young shells from the head of Truckee River, 

 in Lake Tahoe, Placer County, also said to be "found 

 larger by Mr. S. Brannan at about 3,600 feet elevation 

 on the west slope." The latter I understand to have 

 been determined by Tryon himself, and I was thus in- 

 duced to agree with Mr. Carlton, but not having speci- 

 mens to compare, he left the name as P. /lornii with, a (?). 

 Mr. Raymond also obtained some at Quincy, Plumas 

 County, which seem to show the characters of var. 

 disject us, but are a little larger and with whorls a little 

 more convex, also showing more or less irregularity. It 

 is therefore probable that this form inhabits the whole 

 range of mountains, descending at least to 3,383 feet in 

 Plumas County. 



We had considered this as P. hornii, but Mr. Dall, 



