142 Fossil Shells from the Colorado Desert. [ March, 
in great numbers (sometimes in windrows) at various places on 
the surface of the desert. 
Physa humerosa Gould. Natural size. 
One of the species from the well is Physa humerosa Gould, of 
which there is a single specimen; the others, of which there are 
numerous examples, are Tryonia clathrata Stimpson, and Tryonia 
protea of Gould. These latter belong to the family of Rissoide, 
and were described several years ago from specimens collected 
by Prof. Wm. P. Blake. They have also been collected by several 
other parties. From the late lamented Col. Albert S. Evans,’ I 
received, several years ago, half a pint of these desert shells, and 
from others I have received a great number; probably altogether 
as Many as 40,000 specimens have passed under my inspection, 
including the above and a single species of Amnicola (longinqua 
Gould), as well as fragments of a Planorbis and of Anodonta cali- 
forniensis Lea. It is not unlikely that if we had a sufficient quan- 
feet ri D a i 
Tryonia protea and varieties (semi-fossil). Colorado Desert, Cal. From nature, 
: by Stearns. 
tity of sediment from the well, we should find that it contained 
all of these forms. All of the great number of specimens which 
passed under my observation, are in a fossilized or semi-fossilized 
condition, either of a clear opaque white (in this respect resem- 
bling the fossils of the Paris basin), or more or less translucent, 
though more or less silicified, while the delicate sculpture is as a 
perfect as ever. 
The surface of the desert at the point where the well is situated 
is 195.54 feet below the level of the ocean, as indicated by the 
1 Col. Evans was lost at sea, while on his vite from New York to Brazil, ee the 
barning of the steamship Missouri off the Berm 
