CONCHACEA. MOLLUSCA. CYCLAS. 75 



State Coll., No. 285. Soc. Cab., No. 2.';35. 



Cyclas elegans, Adams ; Bost. Journ. J^at, Hist., iii. pi. 3, f. il. 



Shell in its younger stages compressed, in an adult state tumid, 

 sub-globular, the extremities truncated or terminating abruptly, so 

 as to appear somewhat four-sided or rhomboidal ; beaks not prom- 

 inent, the anterior side a very little the shortest and narrowest ; 

 basal margin nearly straight and parallel to the upper margin ; the 

 valves are not regularly convex, but somewhat flattened down the 

 middle, so as to exhibit an obtusely rounded ridge passing from 

 the beaks towards each lower angle ; surface delicately marked 

 with fine, rounded, concentric wrinkles ; color olive-green, with a 

 straw-colored margin, and narrower zones at each stage of growth. 

 Hinge rather strong, the cardinal teeth rudimentary, the lateral 

 ones large and strong. Interior bluish. Length nearly ^ inch, 

 height -^-^ inch, breadth \^ inch. 



Found in a ditch running through the Cambridge meadows, 

 near Fresh Pond. 



This is a remarkable and beautiful species, and seems to be rather 

 rare. Excepting the above locality, I know of no other but at Wey- 

 bridge, Vermont, whence it was sent me by Professor Adams. It is of 

 about the size and width of C. partumeia, but is a very much thicker 

 shell, differently colored and sculptured, and its four-sided, angular 

 outline is quite different. The young of C. similis, though equally 

 four-sided, is much longer proportionally, the color much darker, and 

 the ridges on the surface much coarser. In this species the four sides 

 are nearly equal, 



Cyclas du^bia. 



Shell oblique, triangular-ovate, ])ale-olivaceous, with fine con- 

 centric ridges ; healis hut slightly elevated ; teeth strong, ivhite. 



Figure 56. 



State Coll., No. 286. Soc. Cab., No. 1809. 



Cyclas dilbia, Say; JVicholsons Encyc, Amer. ed., iv. pi. 1, f. 10. 



Shell small, rather thick, triangular, with its corners rounded, 

 shining ; beaks at one end, very little elevated ; hinge margin and 

 short end straight, the two lines forming a right angle ; base and 



