150 Fossil Shells from the Colorado Desert. [ March, 
the easterly flank of the Sierra Nevada, exhibit a consider- 
able variation when compared with those from the preced- 
ing places.1 
The Owen’s river specimens, though inhabiting so elevated a 
station, closely resemble those found at, and in the neighborhood 
of Los Angeles at an elevation of only 280 feet, and the speci- 
mens from both of these places as well as specimens from other 
stations with similar elevations within the southern portion of the 
limits of the coast drainage area of California as shown in Lieut. 
Wheeler’s map, and which stations more closely approximate to 
the level of the desert region, are exceedingly close in their gen- 
eral aspect and minuter characters to the dead shells of the ex- 
tinct lagoons, and to Lea’s type? from the Colorado, presumably 
in the neighborhood of Fort Yuma. At many points within the 
drainage area described in the foregoing reports the Anodonte 
have been detected. 
Iam under obligations to Dr. Edward Palmer for specimens 
from Utah lake, and to Mr. Henry Hemphill for specimens 
from Bear river, also in Utah Territory, These localities are in 
the Wahsatch range, at an elevation of over 4,500 feet above the 
level of the sea. i 
The differences between the specimens from these two locali- 
1 The Owen’s lake has no outlet and is fed by the Owen’s river, a stream about 
thirty feet wide, two feet deep and having a velocity of about five miles per hour. 
As the level of the lake remains constant, there must be perfect equilibrium between 
the amount of evaporation and the incoming water. The lake having one hundred 
and ten square miles of surface, and evaporation of 4.6 feet per year, would suffice 
to swallow up the annual volume of Owen’s river. 
ose who cannot appreciate the amount of evaporation, have invented the hy- 
pothesis of a subterranean outlet, as in the case of the Great Salt Lake in Utah.— 
Wheelers Annual Report, 1876, p. 189. 
? Explanatory of my allusions to variation, herein, as shown by a comparison of 
the Anodons from one place with those from another, to prevent misapprehension I 
should state, that I do not regard variation as exhibited in the West American forms 
under discussion, as of specific value, a conclusion I have arrived at after a long and 
careful study of the relation of variation to environment. While forms or colonies 
of a form belonging unquestionably to the same species, and inhabiting stations pte 
a short distance apart, often exhibit aspects of variation in such a degree 
pear phenomenal, the cause thereof not being immediately obvious, a careful investi- 
gation of the environment frequently rewards us, if not with a full explanation, with 
a clue or a ray of light. 
