Tee AS Ee Pe ee Pe eat eS 
VOLs T.| Variation in Shells. 329 
constant character, so far as I have observed, and one that seems to 
have been overlooked by writers upon our Anodons. 
Habitat, Spokane River, above Post Falls, Idaho. 
Length, from the anterior to posterior end, 2} inches. 
Height, from dorsal to ventral margin, 13 inches. 
Breadth, between valves, 7 inch. 
Mr. R.E. C. Stearns has published an excellent paper on our West 
Coast Anodons, in which he shows by logical arguments and illus- 
trations that the forms we know as Anodonta Nuttalliana, A. Wah- 
lamatensis, A. Oregonensis and A. Californiensis are but varieties, 
or “ expessions of one form,” and closely connected with the Eu- 
ropean A. anatina and A. cygnea. 
I would commend a close study of the facts this paper presents 
to those who believe in the immutability of what they are pleased 
to call species. 
However, I cannot agree with all my friend Stearns writes under 
the head of “ Variability and Uniformity,” when he says: ‘‘ Those. 
species which have the widest distribution exhibit the greatest 
diversity and vice versa. Those which ‘are confined, restricted to, 
or occupy limited areas exhibit little if any variation.” 
“The latter often show a remarkable persistency, and adhere 
with most rigid tenacity to a single aspect of color and form.”’ 
“ Nevertheless there are exceptions to this, for uniformity and 
wide distribution are sometimes exhibited.”’ 
I formerly held the opinions on variation expressed above, and ~ 
they seem to be the general opinion of most of those who write 
upon this subject, but my experience as a collector of American 
shells does not confirm them. 
From observations made in the field the past twenty years, and 
the study of accumulated data, collected and selected for the special 
purpose of investigating and illustrating these very points, I find 
the tendency to vary to be the general condition, and rigidity the 
exception among this class of animals, whether the species has a 
wide geographical range or is limited to restricted areas. Gen- 
erally, and I may say invariably, where we find the most vigorous 
colonies and the largest number of individuals, there we also find 
the greatest diversity, but we sometimes find almost the extremes 
of variation known to a species in localities where individuals are. 
