66 



AMERICAN CORBICULAD^. 



during the spring, and not at all in winter. It inhabits both 

 running and still water, and buries itself somewhat in the mud- 



p. compressum. 



Fig. 69. 



5. Pisidilim variatoile. Prime. — Shell heavy, oblique, inequi- 

 lateral, inflated ; anterior side longer, narrower, somewhat angular at end ; 



posterior subtruncate ; beaks situated pos- 

 teriorly, full, prominent, not approximate 

 at apex ; valves solid, interior light blue ; 

 strise regular, bxit very distinct ; epidermis 

 glossy, very variable, straw color or green- 

 ish-brown with a yellow zone on the basal 

 margin ; hinge-margin curved ; hinge rather 

 slight ; cardinal teeth united, small ; lateral 

 teeth distinct, strong, short. 



Long. 0.21; Lat. 0.18; Diam. 0.17 inches. 

 Hah. North America, in New England, 

 and in the States of New York, Pennsyl- 

 (Cabinets of Jay, Smithsonian Institution, Prime, 



P. variabUe. 



vania, and Virginia. 

 and others.) 



Cyclas nitida, Mighels, Linsley, Amer. Jour. XLVIII, 1845, 276. 



Pisidinm variabile, Prime, Bost. Proc. IV, 1851, 163. 



Pisidium grande, Whittemore, in litt. 1855. 



Muscidium variabile, Adams, Rec. Gen. II, 1858, 452. 



Pisum variabile, Adams, loc. sub. cit. II, 1858, 660. 



This species has hitherto always been looked upon by collectors 

 as the P. virginicum ; but having compared it with the original 

 shells, described as Cijclas dubia, Say, by Dr. Gould, in his Re- 

 port, and with some specimens of F. virginicum 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 become convinced that it is different from Say's shell. 

 Compared with the young of P. virginicum, it is more oblique, 

 less elongated, more inflated, and of a different color. This 

 species is not so elongated as the P. virginicum ; it is more in- 

 flated, the beaks are larger and more tumid, it is also a muc-u 



