332 SYSTEMATIC PALEONTOLOGY 



Occurrence. — Choptank Formation. Governor Eun, Dover Bridge 

 (?) (Dall). 



Collections. — Maryland Geological Survey, U. S. National Mu- 

 seum ( ?) . 



Genus THECODONTA A. Adams. 



Subgenus DICRANODESMA Dall. 



Thecodonta (Dicranodesma) calvertensis n. sp. 



Plate LXXXVIII, Figs. 14, 15, 16, 17, 18. 



Thecodonta ? (Dicranodesma) calverteiisin (Glenn) Dall, 1900, Trans. Wagner Free 

 Inst. Sci., vol. iii, pt. v, p. 1157, pi. xlv, tigs. 23, 24, listed. 



Description. — Shell compact, stout, ovate-triangular, vaulted, very 

 inequilateral; beak acute, slightly projecting and very far anterior; 

 anterior side and end continuous, nearly straight above but meeting the 

 base in a regular curve; posterior side slightly convex; posterior end 

 rounded; base gently curved; muscle impressions rounded, small, nearly 

 equal in size and situated high up; pallial line broad and ragged; ex- 

 terior polished, with fine, faint, irregular, concentric growth stride or 

 with stronger, more remote, concentric undulations; hinge strong, 

 broad; teeth, anterior conical, posterior flattened. 



Length, 4.6 mm.; height, 3.5 mm.; diameter, 1.2 mm. 



Occurrence. — Calvert Formation. Plum Point. 



Collection. — Maryland Geological Survey. 



Genus MONTACUTA Turton. 

 MoNTACUTA MARIANA Dall. 



Plate LXXXVIII, Fig. 19. 



3£ontacuia mariana Dall, 1900, Trans. Wagner Free Inst. Sci., vol. iii, pt. v, p. 1173, 

 pi. xlv, fig. 18. 



Description. — " Shell small, ovate, moderately convex, sculptured 

 chiefly by incremental lines and faint concentric wrinkles; beaks con- 

 spicuous, showing the prodissoconch, but not high, nearly central, the 

 dorsal margin sloping almost equally each way from the beaks, the ends 

 rounded, the base evenly arcuate; hinge with a single, small, subtrigonal 

 anterior lamina in each valve, a small, oblique submaxginal sulcus in 

 each valve behind the beaks; interior of the valves smooth, muscular 

 impressions faint but normal." Dall, 1900. 



