102 



CYCLADID^. 



Cydas similis, Say, Nicholson's Encyc. 1st Amer. ed. ii. pi. 1, fig. 9 (1816). — Be Kay, 

 Nat. Hist. New Yorlc, 222, pi. 25, figs. 264, 263 —Lewis, rroc. Bost. ISoc. Nat. 

 Hist. V. 122; vi. 2. — Also Jay, Adams, Linsley, and Mighels. 



Cydas sulcata, Lam. An. s;ins Vert. v. 560 (1818), 2d ed. vi. 271. — Delessert, Receuil, 

 pi. 7, fig. 3. — Stimpson, N. E. Mollusks, 16. 



Cydas Sarmtucim, Lam. An. sans Vei-t. v. 560 (1818); 2d ed. vi. 271. — Delessert, 

 Keceuil, ])1. 7, fig. 9. 



Cydas fjkjuntea and ponderosa, Prime, Proc. Bo-t. Soc. Nat. Hist. iv. 157 (1851). 



Splueriuin sulcatum, Prime, Pr. Ac. Nat. Sc. xi. 299 (1860) ; xii. 403. 



Cydas rhomhoidea, De Kav, Nat. Hist. New York, 224, pi. 25, fig. 263 (1842). — C. B. 

 Adams, in Thonips. Verm. 168. — Stimpson, Shells of New England, 16. — Lins- 

 ley, Sillini. Joiirn. xlviii. 276. 



For full synonymy see Prime's Synonymy of Cycladcs, in Proc. Acad. Nat. Sc. xi. 299. 



Fig 407. 



S. simile. Eularged. 



Shell sub-oval, nearly equipartite, varying mncli in its outline. 

 In the adult shell the extremities are broadly and nearly equally 

 rounded, the posterior part being somewhat the longest and most 



pointed, the base very little eurved ; 

 valves very convex, remarkal)ly broad 

 across the beaks, which are Imt slightly 

 elevated ; color dark chestnut-brown, 

 within bluish. The young shell is thin 

 and compresh,ed, the hinge-margin nearly 

 a straight line, the extremities truncated 

 so as to give the shell a quadrilateral 

 form ; and the color is a light lemon- 

 color, or honey-yellow. The interme- 

 diate specimens exhiljit all the grada- 

 tions of shape or color between the old and young. Surface at 

 every stage regularly wrinkled concentrically, with strongly raised, 

 sharp lines of growth, and generally a more conspicuous wave mark- 

 ing the former year's growth of the shell ; Ijeaks usually eroded. 

 Hinge with minute, very oblique, cardinal teeth, the marginal ones 

 distinct, strong, and white. Length, seven tenths of an inch ; 

 height, half an inch ; breadth, two fifths of an inch. 



Found in the larger ponds and rivers, especially along the muddy 

 banks of the Connecticut. New England and Northern States. 

 Lachine Canal, Metis Lake (^Be/l)j, Truro, Nova Scotia (^McCul- 

 locli). 



This species is closely allied to the C. rivicola of Europe in slia])e 

 and size ; its raised concentric striae, however, a])pcar to l)e much 

 more prominent. It may always be distinguished by these conspic- 

 uously raised lines, for they are exhibited by no other American 

 species in so great a degree. Several other species are described 



