THE NAUTILUS. 75 
names. Besides, they are not doubtful species, being well defined 
and distributed over wideareas. Mr. E. W. Roper having examined 
specimens wished the writer to publish these species. 
The descriptions will not be exhaustive, especially as to the 
hinges, leaving that, as well as figures, for a monograph, but they 
will be sufficient for recognition of the species. 
P. WALKERI n. sp. Mussel of medium size, elongated, rather in- 
flated, resembling P. abditum, but is smaller than good sized exam- 
ples of that species ; it is also more elongated, and the smaller and 
moderately prominent beaks are more posterior ; thus the anterior 
part is comparatively very long, with the end rounded, the posterior 
quite short, truncated at the end; scutum and scutellum well 
marked. The shell is very thin, translucent, the surface very finely, 
and sharply striated, often somewhat scaly, dullish, or with a silky 
gloss; color grayish, along the margin more or less yellowish horn. 
Hinge moderately strong, of the same type as in Pis. abditum; car- 
dinal tooth of the right valve moderately curved, its posterior part 
thickened and with a deep furrow; below this tooth, there is a deep 
groove formed by the inferior edge of the hinge list raised; and the 
same formation is in the left valve below the deep groove between the 
two cardinal teeth; ligament comparatively strong. 
Long. 4°5, alt. 3°7, diam. 2°8 mill. 
In outline, our species has some resemblance with P. virginicum, 
by its elongate shape, the beaks situated posteriorly, the long and 
below somewhat sacciform anterior part. But it is much smaller, 
its shell quite thin, the hinge finer, the striation finer and the beaks 
are much smaller. 
P. walkeri is quite a characteristic and beautiful species which 
cannot be mistaken for any other. It has a wide geographical dis- 
tribution but seems to live not in great numbers together, as e. g. P. 
abditum, compressum and others do. For the first time I found it 
in a lot of Pisidia from Kent County, Michigan, in the collection of 
Mr. Byrant Walker—in whose honor it has been named—, and in 
another from Utica, Mich. Later it was seen from Grand Rapids, 
Mich. (L. H. Streng), Columbia, Pa. (Bryant Walker), Mohawk, N. 
Y. (in E. W. Roper’s collection, from E, R. Mayo); Clearwater and 
Mississippi rivers, Minn. (H. E. Sargent). 
P. potiruM n.sp. Mussel of medium size, well inflated, rather 
high, beaks slightly posterior, rather high and prominent, not full 
but well rounded ; scutum and scutellum slightly marked. Supe- 
