A Monograph of the Species of Pisidium. 353 
margin curved. Cardinal teeth double, situated nearly in 
the centre; anterior tooth the larger, broader, and more ele- 
vated. Lateral teeth well visible and strong. 
Dimensions. Long. 0.3 ; lat. 0.24; diam. 0.2 inches. 
GEOGRAPHICAL DISTRIBUTION. Norway, Oxford County. 
Maine. (Adams and Mighels.) 
OBsERVATIONS. Compared to the P. variabile Nobis, this 
Species is less oblique, slightly more elongated, less heavily 
Striated, and of a different color; the whole shell is larger 
and stronger. Compared to the P. dubium Gould, it is 
shorter, more inflated; the beaks are more tumid ; the color 
of both the exterior and interior is different ; the hinge mar- 
gin is less curved, and the teeth are not as well developed. 
“The embryo shell is elliptical, obliquely striate, com- 
pressed." (Adams.) Found but rarely; it lives in running 
Waters in company with P. variabile, P. ventricosum, etc. 
In Maine, Dr. Mighels has observed it with C. partumia. 
The so-called C. nitida, from Connecticut and New Hamp- 
shire, is the P. variabile Nobis. 
A 3 
3. Pismiuw autite Anthony. 
Cabinet of the B. S. N. H. 
Pl. Xl Fig. 10, 11, 12. 
Cyclas altilis ANrRoNY. | Adam's Catalogue, 1847, 29. 
Pisidium altile ANtnony, MSS. 
Descrierion. Shell small, ovate, oblique, angular, nearly 
eq ateral ; inferior margin rounded ; posterior and anterior 
gins abrupt ; beaks not large, but ovate and tumid, widely - 
JOURNAL, B, s. N. H. 46 JUNE, 1852. 
