1879. } E Shells from the Colorado Desert. I5I 
ties are these: The river shells present a somewhat more ovate 
outline, are rather more elongated transversely, and are darker 
colored than the lake specimens. These Bear river mussels are 
so exactly like those collected by Mr. C. D. Voy in Washoe lake, 
Anodonta. Bear River, Utah Territory. 
which has an elevation of 4,000 feet in the Sierra Nevada, that 
though the two regions are separated by between seven and eight 
degrees of longitude, if numbers of individuals of the same sizes 
from these two localities were mixed without previous marking, 
they could not be segregated, with any degree of certainty, so 
closely are they alike in form, color, incremental lines and zones, 
which warrants the assumption that the factors of the environ- 
ment are the same at both stations. 
The fragments of Anodontæ, met with in the desert, are por- 
tions of shells (valves) having the same outline as that figured 
and described by Dr. Lea, in 1852,) from specimens collected by 
Dr. J. L. LeConte of Philadelphia, in the “ Rio Colorado, Cali- 
fornia,” and which Lea remarks as closely allied to “ An. nuttal- 
liana” from the “ Wahlamet river, Oregon,” previously described 
by that author.’ 
1 Trans. Am. Phil. Society, 2d Series, Vol. x 
2 Eight species of fresh water mussels have been described from Western North 
America, west of the Rocky mountains and north of Mexico; of these six belong 
to the group Anodonta ; of these six Anodons, four, namely A. nuttalliana, A. wah- 
REPTE A, — and A. cali SNES are regarded by me as varieties - cae 
e species 
In a paper pe the vakion of the fresh. water mussels,” etc., of this western oe 
p i 
region of America, now nearly ready for the press, I point out the features of their 
variation and indicate the influences which have induced it. Seven of ae 
species alluded to, were described by Dr. Lea. 
