110 —- Description of Hight new Species of Shells. 
the distinctive mark of that curious and interesting genus. I 
have only met with it on the Wissahiccon, where it does not 
seem to be very common. 
Genus Pasiryea.—Lea. 
P. sordida. PI. 1, fig. 6. 
P. testa ovato-conoidea, perforata, tenui, albida, diaphana, levi, 
polita; spira obtusa; anfractibus quaternis, convexis; suturis 
sub-profundis ; apertura elliptica, intus alba; columella eri: 
Shell ovately conical, thin, perforated, whitish, diaphanous, 
smooth, polished ; spire obtuse ; whorls four, convex ; sutures some- 
what despi ; mouth elliptical, white within ; cotataaita smooth. 
Length -075. Breadth -025 of an inch. 
Hab. Near Boston. Cabinet of I. Lea. 
Remarks.—I found this shell among a number of specimens of 
Cerithium Sayii, sent to my father by Mr. Adams from Boston. 
It might be mistaken for a very young specimen of Act@on trifi- 
dus, Totten, but that species has the fold on the columella, the 
same shape and the transverse striee, even in its youngest state. 
In the present species, the mouth is acute above and slightly 
rounded below, and is -037 of an inch in length. It may perhaps 
be considered as the smallest of our marine shells yet described. 
- "There has been great confusion among conchologists respect- 
ing the group of shells to which this species belongs. Lamarck 
placed some marine shells in the genus Melania, but the differ- 
ence which must exist between species breathing fresh and salt 
water, would in itself warrant their separation. The genus Hwu- 
lima, Risso, may perhaps embrace the Pasithe@, but in the for- 
mer the mouth is often not effuse, the labrum slightly thickened, 
there are non-secund varices, and the spire is frequently curved. 
Lowe has lately made a genus Parthenia, which only differs 
from Hulima in being white, and having cancellations. This 
does not seem sufficient to warrant a generic distinction. The 
genus Rissoa, Fremenville, closely resembles the Eulima, and 
will also take in part of the Cingula, Fleming, which however 
may be a a from others, by having the lip continuous 
posteriorly. 'T’ Hydrobia, Hartmann, according to Dr. Gould, 
seems to be ch same as the Cingula. The Turritella, La- 
marck, having the mouth non-effuse, is easily separated from the 
rest. The Pasithea differs from these in its effuse mouth and 
acute outer lip. The Niso, meee “satan differs from it in ‘the 
large umbilicus. The Pyramis, Brown, judging from the refer- 
