ir« PALJEONTOLOGY OP NEW-YORK. 



Productella laclii'}iuosa. 



PLATE XXV 

 Stropkomtna iachrymoia : Cosrad, Jonr. Acad. Nat. SciencesPhiladelpbia, Vol. viii, pa. 26G, pl.ll, f. 9. 



Shell ovoid or subhemispheric, semielliptical in outline; the propor- 

 tions varying from nearly equal length and breadth, to width nearly 

 once and a half as great as the length : hinge-line equalling or less 

 than the width of the shell ; extremities angulated or rounded. 



Ventral valve varying from moderately gibbous to vei:y ventricose ; 

 the umbo sometimes a little .elevated above the hinge-line and often 

 extremely elevated and incurved, often flattened in the middle, more 

 or less regularly arching from beak to base, abruptly depressed at the 

 sides of the umbo, and spreading into more or less expanded ears, 

 which are usually deflected, and rarely extend beyond the width of 

 the shell below : basal margin regularly arched, or sometimes nearly 

 straight in the middle. 



Dorsal valve moderately or more deeply concave, following in some 

 degree the curvature of the opposite valve. In some specimens it is 

 nearly flat in the upper and middle portions, and abruptly deflected 

 at the margin. 



Surface of ventral valve (where the shell is partially preserved) marked 

 by fine concentric striae, and, upon the ears, by strong concentric 

 wrinkles, which become obsolete or are but faintly marked on the 

 body of the shell. There is a row of four or five round spines rising 

 from a little below the cardinal margin on each side of the beak ; and 

 surfaces of the casts are [marked by- numerous slightly elongate spini- 

 ferous tubercles, from which rise somewhat slender spines. These spi- 

 niferous tubercles are sometimes principally arranged in lines along 

 partially continuous ridges. The dorsal valve is strongly wrinkled on 

 the hinge-line, and sometimes these marks are continued across the 

 valve in considerable strength; but the specimens examined do not 

 show spine-bases. The casts or impressions of the exterior show pus- 

 tules which indicate fossets on the exterior surface of the shell. 



