MARYLAND GEOLOGICAL SURVEY 285 



Superfamily MACTRACEA. 



Family MESODESMATID/E. 

 Subfamily MESODESMATIN/E. 



Genus MESODESMA Deshayes. 

 MeSODESMA MARIANA n. Sp. 



Plate LXIX, Figs. 1, 2, 3. 



Description. — Shell ovate, depressed, inequilateral; anterior end much 

 the longer; beak very low; anterior side straight; anterior end acutely 

 rounded and much above the line of the base; base a regular curve 

 continuous with curve of anterior end; posterior side and end bluntly 

 curved, meeting the base at an angle on the line of the base; posterior 

 adductor scar compact, oval; anterior scar elongated and largest below; 

 pallial line distinct; pallial sinus moderately deep, rounded; exterior 

 surface somewhat polished with some irregular fine concentric growth 

 lines. 



Length, 9.75 mm. ; height, 6.5 mm. ; diameter, 1.8 mm. 



Occurrence. — St. Mary's Formation. Cove Point, St. Mary's Eiver. 



Collections. — Maryland Geological Survey, Johns Hopkins University. 



Subfamily ERVILIIN/E. 



Genus ERVILIA Tuiton. 



Ervilia PL an at a Dall. 



Plate LXIX, Figs. 4, 5, G. 



Ervilia planata Dall, 1898, Trans. Wagner Free Inst. Sci., vol. ill, pt. iv, p. 915. 



Description. — " Shell small, subtriangular, flattened, smooth or ob- 

 scurely concentrically ridged, subequilateral ; the beaks low, calyculate; 

 the dorsal slopes slightly rounded, subequal; the base evenly arched, not 

 projecting; hinge well developed, the marginal grooves in the right valve 

 almost as long as the dorsal margins ; pallial sinus small, rounded in front, 

 falling considerably short of the vertical from the beaks. Lon. 3.25, 

 alt. 2.25, diam. 1.5 mm." Dall, 1898. 



Occurrence. — Calvert Formation. Church Hill. 



Collection. — Maryland Geological Survey. 



