6o Bulletin 31 60 



Leda plana Lea, PI. 23. Figs. 14-17. 



Nucula plana Lea, Cont. to GeoL Dec. 1833, (Dec.) p. 199, pi 6, fig. 



213. 

 Nucula pulchcyyi Ilia Lea (young sp. ), Cont. to GeoL, '33, p. 84, pi. 3, 



fig- 63. 

 Nuculana plana Con., Amer. Jr. Conch., vol. i, 1865, p. 13. 

 Nuculanaplana Cossmann, Notes Compl. 1893, P- i5- 



Lea's original description, — Shell an obtuse triangle, very transverse, 

 very much compressed, concentrically striate, and transversely folded on the 

 side, sulcate on the umbonial slope, substance of the shell thin ; beaks ob- 

 tusely angular, pointed ; lunule and escutcheon both nearly linear ; anterior 

 series of teeth straight ; posterior series of teeth incurved ; teeth small num- 

 erous, angular ; fosset large, subtriangular ; cicatrices imperceptible ; cavity 

 on the shell very flat, showing the transverse folds ; nacre not pearly. 



Diam. . . . Length . . . Breadth . . . 



A single and imperfect valve onl}- of this species has come under m\- 

 notice. There are however, characters enough remaining to satisf}- me of its 

 being different from those before described. It most resembles th.e. pulcher- 

 rinia. That shell has not, however, the remarkable folds and striae of this 

 species. These stritE, on the anterior part, are combined, two or three to- 

 gether, leaving a furrow between each association. On the posterior part, 

 these striae are single, but disordered by the transverse folds, which exist 

 only on that part of the valve. 



Cossmann evidently found a fragment of this rare species in 

 the barrelfnl of sand he had shipped from Claiborne. 



A fragment in our own collection from the "sand" bed (fig. 

 15) shows the very characteristic markings on the posterior por- 

 tion of the shell, i. e. broad undulations bearing ver3^ finely in- 

 cised concentric lines, — undulations subdividing into two or three 

 folds standing out in strong relief as they pass the imibonal angle 

 and over the post-umbonal slope. 



The beautiful large impression of the exterior of a nearly 

 perfect specimen found on the Neuse River, N. C, has been used 

 for making the gutta-percha cast shown on pi. 23, fig. 14. Here 

 we see the true shape of an adult shell. Note the general lack of 

 folds on the anterior portion and the slight depression or channel 

 extending from beak to anterio-basal margin. The fragment from 

 Claiborne, here enlarged, shows clearly that Lea was correct in 

 saying that the substance of the shell is thin and that the undu- 

 lations show plainly within. This we regard as one of the most 

 beautiful of our Eocene species. It is, however, exceedingly 



