PISIDIUM. 



63 



Fig. 63. 



P. adamsi. 



2. Pisidiuni adamsi, Puime.'— Shell subovate, full, oblique, in- 

 equilateral ; anterior side a little longer, narrower, slightly 

 produced at end ; posterior side broader, somewhat sub- 

 truncate at end, basal margin rounded ; beaks small, a 

 little raised, approximate at apex ; surface smooth, stria 

 very delicate ; color light gray, interior whitish ; hinge- 

 margin curved ; cardinal teeth very small ; lateral teeth 

 very distinct. 



Long. 0.3; Lat. 0.24; Diam. 0.2 inches, 

 Hab. North America, at Norway in the State of Maine, and at Holly, 

 Oakland Co., Michigan. (Cabinets of the Boston Society, Smithsonian 

 Institution, and Prime.) 



Cyclas nitida, Mkjiiels (non Hanley), Bost. Proc. I, 1S41, 48. 

 Pisidiuni adamsi, Prime, Stimp. Moll. New Engl. 1851, 16. 

 Sphxrium nitidum, Deshayes, Biv, Brit. Mus. Cat. 1854, 271. 



A rare species. I have never seen any specimens but those in 

 the collection of the Boston Society and those in my own, all of 

 which came from Professor Adams, who discovered it with Dr. 

 Mighels. The young is elliptical, obliquely striate and com- 

 pressed. The so-called Cyclas nitida, from Connecticut and New 

 Hampshire, is P. variahile. 



Compared with P. variahile, this species is larger, compara- 

 tively more delicate, less oblique, less heavily striated, of a lighter 

 color. It is much more oblique and less elongated than P. 

 abditum. It is more oblique, and more inflated than P. virgini- 

 cum ; it is also more delicate than that species. 



Fig. 64. 



P. adavisi. 



3. Pisidilim aequilaterale, Prime.— Shell small, stout, heavy, 

 somewhat inflated, rhomboidal, subequilateral ; posterior margin a little 



' Not to be confounded with Pisum adamsi of Deshayes, Biv. Brit. Mus. 

 1854, 284, which is the P. jamaicense, Pkimb. 



