356. The American Naturalist. [April, 
To the northward, this seems to be replaced by Anodonta 
kennerlyi, a species closely resembling some of the varieties of 
A. cygnea of Europe, and in Alaska another nearly related 
form, A. youkonensis of Lea, is met with. The latter is an 
absolute synonym of A. herculea Midd., of which specimens ` 
are in our collection, obtained in Kamschatka by Dr. Dall. 1 
had noticed the resemblance of all these forms to that of the 
well known, abundant, variable, and widely distributed Ano- 
donta cygnea and its variety anatina, and on hunting up the 
distribution of that species, I have been able to trace it through 
Northern Asia into Eastern Siberia. Any one who will care- 
fully examine an extensive series of Anodonta cygnea, anatina, 
herculea, youkonensis, kennerlyi, wahlametensis, nuttalliana, oregon- 
ensis, and californiensis, cannot, I think, fail to notice their 
remarkable resemblance in many essential points: the pecu- 
liar and usually exact rounding of the anterior end of the 
shell, the flattening of the umbonal region, which, in good 
specimens, is generally overlaid with hair-like, greenish, radi- 
ating, wavy lines, and the singular cutaway in the posterior 
slope, all indicate close relationship, and the fact that they 
have sprung from a common origin. 
I should unhesitatingly place these forms in a natural 
group, typified by Anodonta cygnea. Dr. Stearns, in the paper 
to which I have already alluded, believes that Anodonta wahl- 
ametensis, nuttalliana, oregonensis, and californiensis, are but — 
variations of the European A. cygnea, and that A. fluviatilis of 
the Atlantic drainage is probably but another form of this 
protean species. 
While I was formerly inclined to this view, a more careful 
and thorough examination of large quantities of material has 
_ induced me to somewhat modify my opinions. Though the 
nuttalliana and its variations are very close to cygnea, I do 
not, at present, feel justified in uniting them specifically, and 
I regard the A. fluviatilis as the type of a rather nearly related 
group, having a distribution from Canada to Florida, in the 
streams which fall into the Atlantic. The shells of this section 
are generally more inflated than those which belong with 
eygnea ; they are not flattened at the umbonal region, and atè 
more full on the dorsal slope. 
