333 SYSTEMATIC PALEONTOLOGY 



Occurrence. — Choptank Formation. Governor Run. Dover Bridge 

 (?) (Ball). 



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

 seum (?). 



Genus THECODONTA A. Adams. 



Subgenus DICRANODESMA Dall. 



Thecodonta (Dicraxodesma) calyertensis n. sp. 



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



Thecodonta V (Dieranodesnia) cidi'erte)isis (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 strise 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. 



Montacuta nuiriana 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 submarginal sulcus in 

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

 impressions faint but normal." Dall, 1900. 



