NO. 1256. FOSSIL SHELLS OF THE COLORADO DESERT— STEARNS. 293 
but little reo^ard to lines of latitude. While altitude, which in this 
connection is equivalent to decreased temperature, has apparently no 
sculptural influence, it seems to bear a close relation to size in the 
Phy.sas. That aspect of depauperation called dwarfing is shown in 
Call's (Table XIV) comparative measurements^ of Physa mnpuUacea 
from Little Gull Lake, in the Mono Basin of California, altitude 7,000 
to 7,500 feet, and Church Lake, near Salt Lake City, Utah, elevation 
I . . 14 95 
about 4,300 feet, the ratio of lengths being- :i— ^— ^ and the ratio of 
I 12,97 
9 81 
widths -^——. The value of this comparison is impaired, first, because 
8.45 
the number of examples from these places is unequal, being only twelve 
from Gull Lake against eighteen from Church Lake, and, second, 
liecause a comparison of this kind to be satisfactory should embrace a 
much larger number of individuals. 
As to the relation between depauperation and salinity, CalTs table 
(XI) giving the mea-surements of thirteen examples of Physa gyriiia 
from ponds near Salt Lake City, elevation about 4,500 feet, and thirty- 
nine specimens from brackish springs at Promontory, elevation 4,900 
feet, the same objections appl3^ His tables (VI, VII, VIII, IX, X, and 
XI), ];ased on comparative measurements of Ponipholyx effusa^ Cari- 
n'lfex newherryi^ Ilelisoina trivolvis^ Limnophysa palustris^ and Physa 
(fyrhia^ indicate, as he says, that "brackish water is correlated with 
depauperation.'"^ While numerous examples of 1\ gyrlna collected 
by Dr. C. Hart Merriam in Bennett Springs, Meadow Valley, Nev^ada, 
elevation 6,0<)0 feet, and the large number (492) of P. humerosa from 
Pyramid Lake, 4,890 feet altitude, after comparison with Colorado 
desert shells of the same species, are afiirmative testimony as to the 
dwarfing influence of higher altitudes (i. e., lower temperature), the 
desert shells being uniformly of larger size. This applies not only to 
the species just named, but to the desert Physas as a whole. Hypso- 
meti'ic or lower temperatures neutralized by thermal conditions, as 
related to size in the I^ysas, is illustrated liy the examples of 1\ gyrina 
collected b}' Dr. Merriam at the Hot Springs in Panamint Valley, the 
shells being fine, large, and dark colored. Here the altitude above the 
level of the desert was not so very great, being about 1,500 feet. CalTs 
Warm Springs, Utah, specimens of P, gyrina var. ellipUca afl'ord a 
similar illustration. "The variet}" " he saj^s, "is found abundantly and 
of large size." The elevation of Warm Springs is over 3,800 feet. 
From the consideration of the relations of sculpture to salinity and 
to thermal waters, of size in connection with hypsometric distribution, 
variation in form as related to environment attracts attention. 
^ A comparison between forms from high altitudes with those from stations nearer 
to the level of the sea would be more satisfactory than that above quoted, where 
both localities are mountain stations. 
^This point discussed elsewliere. 
