PISIDIUM. 67 



smaller shell. Say describes Cyclas dubia as being six-twentieths 

 of an inch in length ; P. variahile is only four-twentieths of an 

 inch in length, and that it is a full grown shell, I am led to be- 

 lieve not only from its heavy striations and mature appearance in 

 general, but also from having found young in the shell. The 

 young is not so oblique as the adult, it is more elongated, less 

 inflated, and of a light yellow color. As a general rule, the 

 coloring of this species varies much in different localities. The 

 specimens collected from llowley, Essex County, Mass., are 

 larger than any I have seen from other places ; their color is also 

 lighter. The animal is remarkable for its want of activity. This 

 is one of our most common species, being found in nearly every 

 stream, and at all seasons of the year, though most plentifully 

 during the spring. 



Fig. 70. 



p. variahile. 



6. Pisidiiim nov-eljoracense, Pkime.— Shell rounded-oval, 



very inequilateral, inflated, margins rounded ; anterior 



side considerably produced, narrower; beaks situated rig. 71. 



posteriorly, large, full, prominent ; valves comparatively 



slight, interior light blue ; striae irregular ; epidermis 



variable, generally greenish -yellow or brown ; hinge- 



marffin a little curved; hinge slight, narrow; cardinal 



P. Tum-eboracense. 

 teeth double, very small ; lateral teeth elongated. 



Long. 0.35 ; Lat. 0.18 ; Diam. 0.13 inches. 

 Hab. North America, in the State of New York. (Cabinets of Smith- 

 sonian Institution, Lewis, Jay, and Prime.) 



Pisidium nou-ehoracense, Prime, Ann. N. Y. Lye. VI, 1853, 66, pi. i, f. 3. 



Pisidhim amplum, Ixgalls in litt. 1855. 



Musculium nov-eboracense,' Adams, Rec. Gen. II, 1858, 451. 



Pisum nov-eboracense, Adams, loc. sub. cit. II, 1858, 660. 



This species, for its size, is comparatively delicate. It seems 

 to be intermediate between P. ahditum and P. variahile ; it is 

 less elongated and more tumid than the former, and less oblique 

 and more elongated than the latter. Found only in two places, 

 at Greenwich and at Mohawk, in the State of New York. 



