211 
trivolvisy and was obtained from Lake Huron by Mr. Racket, 
whose name bad been previously applied in this genus by Brard. 
in the Ann. du Museum, vol. 14. 
It is remarkable that Sowerby has represented this species 
under the name of hicarinatus, apparently without being aware 
that I had previously described it under the same name. PI. 64, 
fig. 3. 
Limneus emarginatus, S. Journ. Acad. Nat. Sci. vol. 2, 
p. 170. 
Ohs. In general obesity it has a resemblance to L. inflatus, 
Brong. It was first sent to me by Mr. Aaron Stone from the lakes 
of Maine. Dr. Bigsby presented me with a specimen which he 
obtained in Upper Canada, and I have recently received several 
from Mr. Titian Peale, also found in Maine, one of which is 
double the size of the figure represented in our Plate 65, fig. 1. 
Limneus catascopium, S. Amer. Ed. of Nicholson’ s Encycl. 
Article Conchology. 
Ohs. Its European analogue is the L. peregrum, L., from 
which it may be distinguished by a deeper fold of the columella, 
and a more acute curvature of the inferior portion of the aper- 
ture. PI. 56, fig. 2. 
Limneus decidiosus, S. Journ. Acad. Nat. Sci. vol. 2,p. 169. 
Ohs. My brother, B. Say, subsequently ascertained it to be an 
inhabitant of Pennsylvania; found also near New Harmony by 
Lesueur. PI. 65, fig. 3. 
Pecten. — Shell free, bivalve, inequivalve, thin, auriculated, 
equilateral ; hinge margin transverse, rectilinear, connected 
throughout by a ligament, the cartilage being inferior, fixed in a 
triangular fosset of each valve, under the apex ; apices contiguous, 
not elevated ; muscular impression large, subcentral ; palleal im- 
pression without sinus : animal suborbicular ; foot very small, some- 
times with a byssus ; mantle fringed with tentacular papillae, of 
which the series is interrupted somewhat regularly by shorter 
cylindrical processes terminating in oculiform disks ; mouth large, 
transverse, surrounded with fringed lobes, and with a thin lamel- 
lated palp on each side ; anus free ; branchiae large. 
Ohs. The numerous species of shells which form this veiy 
beautiful and natural genus, inhabit almost universally the mar- 
gins of the marine portion of the globe, from the torrid zone to 
