66 BuLi^KTiN 31 66 



N'uculana media Con., Am. Jr. Conch., 1865, vol. i, p. 13.. 

 Nucula media Aid., Geol. Surv. Ala., Bull, r, 1886, p. 49. 

 Nuculana media Cossmann, Notes Compl. 1893, p. 15. 

 Leda media Dall, Trans. Wag. &c., 1895, p. 578. 



Lea's original description. — Shell elliptically transverse, somewhat 

 inflated ; rounded before, produced and truncated behind, equilateral, fur- 

 nished with fine concentrical folds in the middle and three ribs on each 

 valve behind ; anterior part smooth ; substance of the shell thin ; lunule 

 none ; beaks very small, pointed ; anterior series of teeth arched— posterior 

 series inflected ; teeth small, pointed, angular, diminishing in size towards 

 the beak ; fosset scarcely perceptible ; cicatrices obsolete ; cavity of the 

 shell rather shallow, having its channel interrupted by a callus ; margin en- 

 tire ; nacre not pearly. 



Diam. .i, Length 3-2oth«, Breadth 7-2oths of an inch. 



The folds are minute and remarkably regular. Becoming obsolete as 

 they approach the anterior margin, they there vanish altogether as if erased 

 by attrition. These folds terminate posteriorly very abruptly at the first 

 rib, of which there are three on each valve, passing from the beak to the 

 posterior margin. The central rib is the largest and disposed to imbricate. 

 A remarkable callus is placed directly in the channel of the posterior part of 

 the shell. It is disposed to be polished inside and out. 



Two Specimens in a tray in the Conradian collection at the 

 Academy prove that as Conrad remarks (Am. Jr. Conch. 1865, 

 vol. I, p. 191 b) that Lea's media is equivalent to his equalis. But 

 the description he gives of the shell (Foss. Sh. Tert. Form., p. 

 46) is quite unrecognizable, Idea's figure and description are re- 

 markably correct. De Gregorio on pi. 3 of his Claiborne work 

 has given some very poor and incorrect figures of this species. 



Of the three posterior "ribs" mentioned bj^ Lea, the inner 

 is the least conspicuous and it extends but half way to the poster- 

 ior termination of the shell. 



Type.—l^o. 541 1, Phila. Acad. Coll. 

 \ Specimens figured. — Paleont. Mus., Cornell Univ. 



Localities and horizon. — St. Ma^crice : Lisbon (slender var- 

 iety, fig. 4) ; Marble Quarry, La. Claiborne : Claiborne sands. 



Leda catasarca Dall, PI. 25. Fig. 5, a. 



Leda catasarca Dall, Trans. Wag., Ill, '95, p. 588. pi. 32, fig. 13. 



Dall' s original description. — Shell small, very plump, nearly equilat- 

 eral, concentrically sculptured, with on the beaks and body rather wide, flat- 

 tish riblets, more crowded ventrally, obsolete dorsally behind and on the 



