MARYLAND GEOLOGICAL SURVEY 667 



impressed above the middle of the shell about half-way between the 

 top of the umbonal prominence and the posterior cardinal extremity. 

 Muscular impressions large, the anterior ones deeply impressed, the pos- 

 terior ones scarcely or not at all differentiated from the surface of the casts. 

 The left valve with two strong cardinal teeth beneath the beak with a pit 

 between, right valve with a single cardinal tooth; anterior lateral teeth 

 more remote from the cardinal teeth than the posterior ones, and also 

 apparently much stronger. Inner free margin of the valves crenate along 

 the posterior margin, smooth along the basal and anterior margins. Sur- 

 face of the shell marked by radiating ribs upon the posterior slope, which 

 in the internal casts at least, continue only from the margin up to the 

 umbonal prominence; central and anterior portions of the shell marked 

 by concentric lines of growth only. Both of the species described by Whit- 

 field from New Jersey as Cardium perelongatum and Pachycardium bur- 

 lingtonense, are certainly internal casts of the shell described by Conrad 

 from Mississippi as Cardium spillmani, the example to which the last two 

 names was applied being an exceptionally broad specimen. The species 

 is for the most part restricted to the Navesink marl, where it attains its 

 maximum size. The specimens which have been rarely noticed in the 

 Merchantville clay are usually small, although Whitfield's P. burling- 

 tonense is a very large example." Weller, 1907. 



The species is represented in Maryland merely by imperfect casts, one 

 of which must have been, when perfect, fully 115 mm. in altitude. 



Occurrence. MATAWAN FORMATION. Post 105, Chesapeake and Dela- 

 ware Canal, Delaware. MONMOUTH FORMATION. Bohemia Mills, Great 

 Bohemia Creek, 1 mile southeast of Bohemia Mills, right bank of Bohemia 

 Creek between Scotchman's Creek and Bohemia Ferry Bridge, Cecil 

 County, Maryland. 



Collections. Maryland Geological Survey, Philadelphia Academy of 

 Natural Sciences, New Jersey Geological Survey, U. S. National Museum. 



Outside Distribution. Matawan Formation. Merchantville clay marl, 



New Jersey. Monmouth Formation. Navesink marl, New Jersey. Black 



Creek Formation. North and South Carolina. Peedee Formation. 



North and South Carolina. Eutaw Formation (Tombigbee sand mem- 



44 



