LAMELLIBRANCHIATA OF THE LOWER MARLS. Ill 



Genus NUCULARIA Conrad. 



(Am. Jour. Concb., Vol. Y, pp. 44 and 98 (name mentioned only).) 



Nucularia papyiia. 



Plate XI, Figs. 18-20. 



Nvcularia papyria Conrad. Am. Jour. Conch., Vol. V, p. 44, PI. I, Fig. 7, p. 98, PI. 

 IX, Fig. 25. 



The shells of this species are quite small and very ventricose, especially 

 in the anterior half, and becoming rapidly depressed posteriorly. The 

 largest individual present in the collection barely exceeds three-eighths of 

 an inch in length. The form is irregularly^ subovate, a very little wider 

 across the shell opposite the beaks than elsewhere. Beaks very small and 

 obscure, located at about the anterior third of the length and incurved. 

 Hinge-line nearly straight behind the beaks, but rather rapidly declining 

 in front and rounding into the curvature of the anterior end. Basal margin 

 subparallel to the posterior part of the hinge-line, and the posterior end 

 rounded above and obliquely truncate or rounding forward below, so as to 

 materially shorten the basal line. Surface of the shell polished, but marked 

 by exceedingly fine concentric lines of growth. Hinge-plate very obscure, 

 and its characters mostly unknown or extremely doubtful. A fragment of 

 a shell in the collection, labeled by Mr. Conrad as of this species, shows 

 five small teeth, which appear to represent the anterior section of the hinge- 

 plate, and a cast of a right valve shows that the posterior part has had a 

 single long lamelliform tooth parallel to the margin of the shell. No evi- 

 dence of transverse teeth on this part appears. Muscular impressions and 

 pallial line entirely invisible. Substance of the shell dense, but not 

 nacreous. 



There are eight individual valves or casts of valves of this species 

 before me, besides the fragment showing hinge-teeth, but none of them are 

 in a condition to remove the doubt concerning the hinge structure. It 

 appears to me quite doubtful if the specimen showing teeth really belongs 

 to the same species. The fragment is not nearly so much curved as would 

 be a fragment of equal size from any one of the specimens here present, and 

 moreover, the piece is attached to a second fragment by a bit of paper 



