_ Mollusca of Middlebury, Vt. and. Vicinity. 267 
rarely in Lake Champlain. Deshayes could not have suggested, 
as he has, (2d edit. Lam. An. sans Vert. in loc.) that this is the 
young of P. ponderosa, Say, had he seen suites of young and 
old in both species. This species is more nearly related to P. in- 
tegra, Say, from which it is well distinguished by Haldeman, 
(Monog. Limniad. No. 1.) 
P. lustrica, Say. This species is vety abundant in Lake 
Champlain and in the streams. Its color varies from brown to 
green in different localities. 
VALVATA. | 
V. tricarinata, Say. Abundant in Lake Champlain, of a grass 
green color. 
V. sincera, Say. This species occurs plentifully in Putts’s 
swamp, on the New York side of Lake Champlain, opposite Brid- 
port. It is so rare, that a description of the animal may not be 
without interest. 
Foot whitish, swelling and regularly rounded posteriorly, with 
the anterior lobes sharply angular, somewhat contracted in the 
middle, less than .3 in. long; head anteriorly obtuse and bilobed, 
—lobes regularly rounded,—whitish, with a tinge of slate color 
on the top, deepening posteriorly ; mouth pale-yellowish ; tenta- 
cles flifowia whitish, more than .2 in. long ; eyes minute, black, 
shining, situated on the upper and outer part of the posterior side 
of the protuberance at the base of the tentacles ; branchial cavity 
blackish brown on the margin; plumose branchia consisting of a 
stem, on each side of which extend, at right angles to it, about 
ten filiform obtuse branches, bent in zigzag, shorter near the top, 
the whole appearing like a feather ; tentaculiform branchia rather 
longer than the tentacles, equally slender and obtuse. 
Limnza. 
L. megasoma, Say. This large and rare species I have seen 
only at Burlington. 
. appressa, Say. 'This species has been found only in or 
near Lake Champlain. At Burlington itiscommon. Sometimes 
it is nearly as much shouldered on the body whorl as the L. siag- 
nalis of Europe, from which it differs very slightly. 
L. gracilis, Jay. This very remarkable species occurs in Lake 
Champlain. About half a dozen specimens were discovered near 
Burlin ton, and have been distributed by Prof. Benedict. A sin- 
gle specimen, large and perfect, but without the animal, I found 
