224 NEW-YORK FAUNA — MOLLUSCA. 



Color. Young, light waxen, passing into greenish horn in the adult, with bluish white or 

 yellowish white on the margin. Animal, light pink. 



Vertical axis, 0" 3 - 0*45 ; transverse ditto, 0'45 - 0*6. 



This species is common in swamps and sluggish streams in every part of the State. Its 

 hitherto ascertained geographical range is from Massachusetts to Ohio. I agree in opinion 

 with Dr. Gould, that the varieties 2 and 3 of the Cycla de cornee accord perfectly with our 

 species. 



Cyclas rhomboidea. 



PLATE XXV. FIG. 263. 



(STATE COLLECTION.) 



Cyclas rhomboidea. Say, Jour. Acad. Nat. Sciences, Vol. 2, p. 330., 

 C. id. Adams, Am. Jour. Sciences, Vol. 40, p. 277. 



Description. Shell solid, transversely elongated, subequilateral, rhombiform ; the basal 

 margin regularly curved, approaching a straight line. Beaks not greatly elevated, contiguous, 

 often decorticated. Anterior margin subtruncated ; the posterior margin obtusely rounded. 

 Two cardinal teeth in each valve, oblique with an intermediate pit ; the anterior smallest : 

 the lateral teeth distinct, bipartite at each extremity. Surface polished, with minute concen- 

 tric striae : cavity with faint impressed incremental stria?. 



Color. Epidermis olive-green to light chesnut ; within opake white. 



Vertical axis, 0*45 ; transverse ditto, 0*7. 



I refer to this species specimens procured from Rockland county by Dr. Budd, and from 

 Lake Champlain. They are remarkable for their polished surface and rhomboidal outline. 

 The dimensions given above are larger than those of Mr. Say. 



Cyclas elegans. 



Cyclas elegant. Adams, Am. Jour. Vol. 40, p. 277. Id. Bost. Jour. Vol. 3, p. 330, pi. 3, fig. II, 

 C. id. Gould, Invertebrata of Mass. p. 74, fig. 55. 



Description. Shell rhombic-orbicular, compressed in the young, much inflated in the adult ; 

 the extremities subtruncated, so as to appear rhomboidal. Beaks nearly central, not promi- 

 nent. Surface with fine concentric stria? ; the valves not regularly convex, but somewhat 

 flattened down the middle, so as to produce a slight elevation from the beaks to the anterior 

 and posterior portions of the basal margins. Cardinal teeth rudimentary, very thin ; lateral 

 teeth strongly developed. Basal margin nearly straight. 



Color. Epidermis olive-green, with a straw-colored marginal zone, and narrow zones at 

 the different stages of growth ; within bluish white. 



Vertical axis, 0*35 ; transverse ditto, 0*5. 



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