MARYLAND GEOLOGICAL SUEVEY 401 



NUCULA PRUNICOLA Dall. 

 Plate CVIII, Figs. 12, 13, 14. 



Nucula prunicola Dall, 1898, Trans. Waguer Free Inst. Sci., vol. iii, pt. iv, p. 576 

 pi. xxxii fig. 9. 



Description.— " ^\iQ\\ small, inflated, polished, very inequilateral; sur- 

 face with obsolete, obscure radial striag, strong where they cross between 

 the concentric ridges and near the ventral margin ; beaks, dorsal slopes, 

 escutcheon, and the posterior two-thirds of the sides of the shell smooth 

 or nearly so ; on the anterior third sculpture of moderately elevated con- 

 centric lamella separated by wider radially grooved interspaces; these 

 lamellae break off abruptly anteriorly, and posteriorly become gradually 

 obsolete in front of the middle of the shell; they are strongest in front 

 and near the margin; lunular area lanceolate, large, not impressed, 

 marked by the cessation of the lamellae; escutcheon roundly cordate, im- 

 pressed; the margins pouting in the middle; there is no circumscribing 

 line ; beaks turgid, recurved ; interior brilliantly pearly, the basal margin 

 strongly crenulate, the muscular impressions feeble; base arcuate, ends 

 rounded; chondrophore narrow, not prominent, anteriorly directed; the 

 anterior line of teeth long, slightly arched, the posterior meeting it at 

 nearly a right angle, short, straight; anterior teeth about twenty; poster- 

 ior six or seven. . . ." Dall, 1898. 



This species may be readily distinguished by the concentric ridges or 

 raised lamellae on the anterior third of the shell. 



Length, 6 mm.; height, 4.5 mm.; diameter, 3.7 mm. 



Occurrence.— Calvert Formation. Chesapeake Beach, 3 miles 

 south of Chesapeake Beach, Plum Point. 



Collections. — Maryland Geological Survey, Johns Hopkins University, 

 U. S. National Museum. 



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