358 CALIFORNIA ACADEMY OF SCIENCES. 



ford, about lat. 39° 25', although the summer mouths are 

 warm aucl moist, uo traces of them were found. As the 

 permanent snow is no doubt proof of a nearly constant 

 night temperature of 32°. and frosts are frequent during 

 summer down to 6,000 feet, we may consider these as the 

 causes of the absence of any mollusca. It is evident that 

 this limit must vary much in different parts of the moun- 

 tains, as snow does not lie permanently below 10,000 feet 

 on Mt. Shasta, lat. 4P 28', nor below 11,700 feet on the 

 "High Sierra," lat. 36° 30' to 38°, according to late explora- 

 tions of the U. S. Geol. Survey. 



The wide gap in the northern Sierra referred to in the 

 last article (Bull. IV, p. 251), in which no land-shells were 

 known to exist for 100 miles north of Yuba river, has been 

 partly bridged over by the discovery of several at Quin- 

 cy, Plumas County, by Mr. W. J. Raymond. At an alti- 

 tude of 3,383 feet, or near it, he found (1) a Mesodon 

 (Aplodon) called by Mr. Binney an aberrant form of M. ar- 

 onigerus Ancey, or possibly new (no doubt the one reported 

 as '' Columbianus " from Calaveras Big Trees). Also (2) 

 Patala (stiiateUa?) cronkhitei Newc, (3) PiqjiUa corpulenta 

 Bid., (4) Vitrlna pfelfferi Newc, (5) Succinea oregonensis 

 Lsa. (6) S. naUaUianaJjQB.., (7) S . stretcliiana Bid. That ele- 

 vation is therefore about the dividing line between the large 

 and small groups near lat. 40'^. It is true tliat none of the 

 large banded species occurred, as they do up to 5,000 feet 

 toward the south, but No. 1 belongs to a medium -sized 

 group more numerous toward the north, while Nos. 2, 3, 4 

 and 7 are all of the subalpine group in California, and 5 and 

 6 rare in the lower Sierras, though common near the coast 

 up to 3,000 feet. Several of them were before known from 

 the same county and southward; in fact all except Nos. 1, 5 

 and 6. 



Respecting " Macrocydis ^' Vancouver ensis from the Sierras, 

 mentioned on p. 247, I have seen dead shells apparently of 

 that species from Calaveras County, near Cave City at 



