514 Systematic Paleontology 



Collections. — Maryland Geological Survey. Philadelphia Academy of 

 Natural Sciences, New Jersey Geological Survey. 



Outside Distribution. — Nucula slackiana Gabb. Magothy Formation. 

 Cliffwood clay, New Jersey. Matawan Formation. Merchantville clay 

 marl, Marshall town clay marl and Wenonah sand, New Jersey. 



Nucula amica n. sp. 

 Plate XIX, Pigs. 5, 6 



Description. — Shell nacreous, small, moderately heavy, transversely 

 ovate-trigonal in outline, umbones small, feebly inflated, inconspicuous, 

 opisthogyrate, slightly posterior in position, lunule elongated, defined by 

 the angulation of the valve and by the partial evanescence of the external 

 sculpture ; escutcheon large, cordate and appressed, defined by the abrupt 

 evanescence of the disk sculpture, smooth excepting for a couple of sulca- 

 tions subparallel to the dorsal margin ; anterior end more produced than 

 the posterior, obscurely angulated at the ventral margin, posterior end 

 obliquely truncated, base line feebly arcuate; external surface sculptured 

 with approximately forty concentric ridges uniform in size and spacing, 

 obtuse and asymmetrical; their dorsal slope steeper than their ventral; 

 entire exterior exclusive of the lunule and escutcheon overridden by very 

 faint, microscopically fine radial lirations separated by interspaces of equal 

 width; ligament internal, lodged in a chondrophore which extends 

 obliquely forward from beneath the umbones; teeth very fine, even and 

 close-set, slightly V-shaped ; characters of adductors and pallial line lost ; 

 inner basal margin finely erenate. 



Dimensions. — Altitude 6 mm. ; latitude 8 mm. ; semi-diameter 2.3 mm. 



Type Locality. — One mile west of Friendly, Prince George's County. 



Nucula amica is described from very much battered valves, but the 

 sculpture is so unique that it justifies the introduction of the form into 

 the literature. 



Occurrence. — Monmouth Formation. Brightseat, 1 mile west of 

 Friendly, Prince George's Count}'. 



Collection. — Maryland Geological Survey. 



