NO. 1256. FOSSIL SHELLS OF THE COLOR A DO DESERT— STEARNS. 279 
Here we find the southerly ran^e extending- 1,800 miles from the 
Colorado desert, as before mentioned, and the occurrence of this form 
is corroborated and its presumable wide dispersion in that country 
shown b}' Frauenfeld's examples from Durango. The Michoacan and 
Diirango shells, like the Death Valley specimens, lielong to the smooth 
variety which occurs with the other varietal facies in the Colorado 
region of California. 
This smooth form has recently been detected by Dr. Pilsbry ^ in some 
fiuviatile debris from South Spring Creek, near Roswell, New Mexico. 
Orcutt's Fish Spring examples are finely granulose. I am further 
indebted to Mr. Orcutt for several specimens, recently received, that 
were detected by him living in the Dos Palmas Springs. The Dos 
Palmas shells vary from individuals with a smooth surface to those 
that are sculptured by fine revolving- threads. 
The Sevier Lake (middle Utah) specimens collected by Dr. Yarrow 
in 1S72 are so much weathered as to efface the sculpture. It should 
be borne in mind, however, that the Yarrow specimens are so few in 
number that it would be quite unsafe to assume that many other 
varietal aspects do not occur at the Bonneville localities.^ 
The collection made by me in 1882, now in the U. S. National Mu- 
seum, included some 40,000 examples of Paludestrina from the surface 
of the desert at the localities known as Indio, Walters, Dos Palmas, 
and Volcano Springs. These stations are all within the great depres- 
sion, being, respectively, 20, 195, 253, and 225 feet below sea level. 
At these places several hundred specimens of the pond snails Physa 
were collected, as well as a few examples of Paludestrina Jonglnqua 
{^Amnicola longinqua Gould), for which no special search was made. 
A dwarfed aspect of Fluminlcola {coliwihiana) occurs occasionally, 
and two or more species of Planorhls are met with, but the absence 
of any form of the genus Limncea is noteworthy. 
In considering the principal varietal features of P. protea^ we may 
conveniently group them as follows: 
VARIATION IN FORM. 
First. It is seen that some individuals are much more attenuated than 
others. In certain instances the shells are quite robust as compared 
with length, the basal whorl being conspicuously larger and forming 
nearly two-thirds of the total length as compared with five-ninths or 
much less than one-half in other specimens. In diameter the extremes 
are as 13 to 20. 
' Nautilus, XIII, November, 1899, p. 79. 
^ P. protea was not detected by Call in the Lahontan region, its place being appar- 
ently taken by Pyrgulopsis nevadensis, which, though not found in the Lahontan 
beds, occurs in countless thousands living in Pyramid Lake as well as in Walkers 
Lake (dead only?). 
