632 SYSTEMATIC PALEONTOLOGY 



Outside Distribution.- Magothy Formation. Cliffwood clay, New 

 Jersey. Matawan Formation. Merchantville clay marl, Woodbury clay, 

 New Jersey. 



PHOLADOMYA CONRADI n. sp. 

 Plate XXXVIII, Fig. 1 



Pholadomya occidentalis Conrad, 1860, Jour. Acad. Nat. Sci., Phila., 2d ser., 



vol. iv., p. 276. 

 Pholadomya occidentalis Owen, 1860, 2d Kept. Geol. Recon. Ark., pi. viii, 



fig. 9. 



Description. " Subovate, very inequilateral, inflated anteriorly ; ribs 

 about twenty-five, irregular, prominent, acute, posteriorly distant, crenu- 

 latecl by rugose concentric striae, on the umbo tuberculato-crenate ; 

 summit very prominent; anterior margin obliquely truncated. Length 

 3 inches, height 2| inches.'' Conrad, 1860. 



Type Locality. Tippah County, Mississippi. 



Shell very thin and nacreous, approximately equivalve, very inequi- 

 lateral ; umbones rather narrow and compressed, obtusely angulated, rising 

 high above the dorsal margin, almost at the anterior extremity ; anterior 

 end broadly and very feebly arcuate; posterior end symmetrically pro- 

 duced and strongly arcuate; external surface sculptured with twenty-five 

 or twenty-six sharply elevated radial lirae, beaded in the umbonal region 

 by the intersecting incrementals and minutely undulated by the growth 

 sculpture even to the ventral margin. 



Pholadomya conradi n. sp. has been confused with P. occidentalis 

 Morton, so characteristic of the Xew Jersey and Delaware Matawan. The 

 later species (P. conradi) runs smaller and is less inflated in general out- 

 line, while the very high, rather narrow, subangulated umbones, rising 

 from the extreme anterior end of the shell, lend it an aspect that is very 

 characteristic and quite distinct from the subcylindrical outline of P. occi- 

 dantalis Morton. 



Occurrence. MONMOUTH FORMATION. Brightseat, Prince George's 

 County. 



Collections. Maryland Geological Survey, U. S. National Museum. 



