MARYLAND GEOLOGICAL SURVEY 621 



gin quite strongly rounded, obliquely produced at the base ; ventral mar- 

 gin somewhat oblique to the dorsal; posteriorly produced, in many indi- 

 viduals feebly and broadly contracted medially ; basal constriction due to 

 the broad and very shallow depression of the valves in front of the obtuse 

 posterior carina which is initiated at the umbones and most prominent at 

 its origin, becoming feebler and finally evanescing about half-way to the 

 posterior ventral margin; external surface sculptured with sharp, rather 

 distant and irregularly spaced incremental lirations which tend to become 

 obsolete upon the medial portion of the shell; characters of interior of 

 shell not known. 



Casts of this small form are not rare in the Upper Cretaceous of Mary- 

 land, although the shell is so thin and so flaky that it has not been found 

 possible to secure any fragments large enough to give the hinge dentition, 

 yet the exceedingly thin and very highly nacreous shell and its general 

 outline suggest Lithophaga rather than Modiolus. The form is much 

 more compressed than L. ripleyana Gabb, the umbones more flattened and 

 the posterior carina more angular. Furthermore there is no evidence 

 that a calcareous encrustation was ever developed as in the Kipley species, 

 but rather that it buried itself in the soft muds near the shore. 



Whitfield's restoration of Gabb's type is probably inaccurate as the 

 material is much crushed and the original outline obscure. 



Occurrence. MOXMOUTH FORMATION. Brightseat, Brooks estate near 

 Seat Pleasant, Prince George's County. 



Collections. Maryland Geological Survey, Philadelphia Academy of 

 Xatural Sciences, New Jersey Geological Survey. 



Outside Distribution. Matawan Formation. Merchantville clay marl, 

 and Woodbury clay, New Jersey. 



LITHOPHAGA LINGUA n. sp. 

 Plate XXXVI, Fig. 14 



Description. Shell small, compressed, not very thin, transversely and 

 somewhat obliquely ovate in outline; umbones anterior, almost but not 

 quite terminal, well rounded, but not conspicuously inflated, proximate, 



