THE NAUTILUS. aly 
Columbia river, Oregon and which the former named U. oregon- 
ensis, discribing and figuring it in Trans. Am. Phil. Soc. X, p. 275, 
pl. 22, fig. 33. The specimen is in bad condition, being somewhat 
broken and considerably eroded. Ina paper on the Relationships 
and Distribution of the North American Unionide, with notes on 
the West Coast Species, which I published in American Naturalist, 
Vol. XX VII, No. 316, I stated that I had come to the conclusion 
that the specimen in question was a form of the widespread and 
variable Unio luteolus Lam, there being examples in the National 
Museum from Canada very much likeit. I believed that if it really 
came from the Columbia river it was just possible the young might 
have been carried in mud on the feet of aquatic birds, from waters 
near by which drain into the Missouri, in which stream U. luteolus 
is found. But I have never been quite satisfied with my determina- 
tion of the shell, since it always seemed to resemble to some extent 
a group of the Mexican species. To-day, in carefully going over 
all the Mexican and Central American Naiad material in our own 
and the Lea collections I suddenly discovered a surprising resem- 
blance between the Lea specimen and some others of U. rowelli Lea, 
and on careful comparison I found it to be undoubtedly an old, solid, 
and inflated female of that species. 
Unio rowelli is a remarkably variable form which I cannot for a 
moment doubt is exactly synonymous with U. maeneilii Lea, the 
types of both species being in the Lea collection. Lea calls atten- 
tion in his description to its resemblance to U. sapotalensis, to which 
it is closely related, and it may be remarked in passing that in this 
group the females and males are separate, the former being inflated 
in the posterior ventral region like those in the Luteolus Group. 
Some specimens of this protean species are much inflated, others are 
compressed ; some are somewhat triangular and pointed at the base 
of the posterior slope, without a trace of biangulation, others are 
nearly rhomboid and distinctly biangulate; there is considerable 
variation in the degree of sulcation, and in the coloring of the epi- 
dermis. They may be either uniform greenish-yellow, brownish, 
or marked with distinct and delicate radiating stripes asin the type 
of U. oregonensis. And all these variations may occur in a lot from 
a single locality. 
The cardinals are rather compressed, double in the left and single 
in the right valve, and have a peculiarly rough, torn appearance ; 
while the laterals are somewhat striated longitudinally. 
