A Monograph of the Species of Pisidium. 351 
DESCRIPTION OF THE SPECIES. 
y LI 
l. PISIDIUM VARIABILE Nobis. 
Cabinet of the B. S. N. H. 
PL XL Po 559 
Pisidium variabile Nogis. Bost. S. N. H. Proc. iv. 163. 
Description. Animal. Foot rather short and thick, issu- 
ing from the immediate inferior opening of the mantle. Sy- 
phon short, 
Shell stout and heavy, very oblique, rather inflated than 
otherwise; posterior subtruncate ; beaks large, prominent, 
not approximate; margins rather abrupt; striations very 
heavy and irregular; color dark olive green with a zone of 
yellow on the margins; interior blue; hinge margin gently 
curved ; cardinal teeth united, small ; lateral teeth prominent. 
Dimensions. Long. 0.21; lat. 0.18 ; diam. 0.179 inches. 
GEOGRAPHICAL DISTRIBUTION. Portland, Me. (Mighels.) 
Cambridge Meadows. Rowley, Essex County, Mass. (No- 
bis) New Hampshire, (Steele.) „Manhattan Island, N. Y. 
(Nobis.) ^ Lake Champlain and Lake George, (Nobis.) 
Greenwich, Washington County, N. Y. (Ingolls.) Connec- 
ücut, (Linsley.) Groton, Mass. (Lewis.) Virginia, (An- 
thony.) 
Ogsrrvations. This species has hitherto always been 
looked upon by collectors as the P. dubium Gould, but hav- 
ing compared it with the original shells, described as Cyclas 
dubia Say by Dr, Gould, in his Report, and with some spe- 
cimens of P, dubium from Westfield, Mass. sent to me by 
Prof. C. B. Adams, as well as with some others sent to me 
from Philadelphia, by Prof. S. S. Haldeman, I have come to 
the conclusion that it is different from Say’s shell. Com- 
Pared to the young of P. dubium it is more oblique, less 
elongated, more inflated, and of a different color. This 
po Spiel les is not so elongated as the P. dubium ; rmt. 
