1018 On the Shells of the Colorado Desert October, 
The typical form of Physa humerosa may be stated in brief as 
being rather short and stumpy, the upper part of the last or basal _ 
whorl flattened or tabulated, with a small, low, slightly elevated 
apex, as a whole presenting a somewhat obtuse triangular aspect, 
Its next of kin, geographically, is P. virgata, which is a rather 
elongated form with an elevated spire. “ale! 
Now the Indio lot exhibits some examples more triangular in 
general outline and more tabulated or flattened above than the 
typical or even ordinary Aumerosa, and variation also in the direc- 
tion of virgata, and still other specimens passing, by way of said 
species, to still greater elongation and elevation of the spire. Within — 
these extremes of variation we have also a connecting link with — 
the widely distributed and abundant P. heterostropha, which Bin- 7 
ney! credits to Utah lake on the testimony of Capt. Burton's — 
specimens in the Smithsonian collection, which brings that spe 
cies within the drainage area of the Colorado river, and indicates — 
the path of migration to the desert region wherein Indio and 
Walter’s stations are situated. = 
Besides the forms and thcir varieties as above, we have extreme a 
variation amounting to distortion in several instances—all point- — 
ing to this (Indio) locality as a most interesting region whereit 
to study the phenomena of variation in this class of shells. a 
In my recent paper on the Fresh-water Mussels, etc,” z3 
particularly in that portion on the circumboreal distribution 
certain fresh-water gasteropods, I refer to the Ameri 
stropha as representing the European P. fontinalis ; 
tion or intimacy of these various alleged species, as l 
rial from new localities comes to hand, is evidently of great 
portance as throwing additional light on geographical distr 
and physico-geographical conditions. 
* While Mr. Binney regards many of 
scribed as synonyms, and so places them int 
have referred; he often gives but a single figu 
species as he regards as valid, and which inclu 
synonyms, cy 
The variability of the pond snails is so excessive | 
quite impossible to present the protean facies they display © 
0 
the species heretofore 
he work to wai 
re to illustrate 
de certain of 
1 L. and F. W. Shells of N; A., p. 89. 
2 Nov. 20, 1882, Proc, Cal. Acad. Sciences, “ On the History and 
the Fresh-water Mussels,” &c., &c. 
