MARYLAND GEOLOGICAL SURVEY 303 



Description. — " Shell solid, ovate, distorted more or less by the irregu- 

 larities of its situs; posterior end blunt, longer; anterior end shorter, 

 rounded; sculpture of fine, nearly uniform radial rounded threads with 

 wider interspaces, crossed by fine, rounded, slightly elevated incremental 

 lines; beak moderately elevated, hinge short, with, in the left valve, one 

 strong, apically grooved cardinal between two simple narrow diverging 

 teeth; ligamentary nymph short, strong, deeply grooved; basal margin 

 feebly crenulated by the external sculpture; pallial sinus wide, shallow." 

 Dall, 1900, 



Length, 20 mm.; width, 23 mm.; diameter, 7 mm. 

 Occurrence. — Choptank Formation. Governor Eun, 2 miles south 

 of Governor Eun, Jones Wharf, Dover Bridge. 

 Collection. — Maryland Geological Survey. 



Section PETRICOLARIA Stoliczka. 



Petricola calvertensis Dall. 

 Plate LXXIII, Pigs. 10, 11, 12. 



Petricola (Petricolaria) calvertensis Dall, 1900, Trans. Wagner Free Inst. Sci., vol. iii, 

 pt. V, p. 1060, pi. xliv, fijr. 14. 



Description. — " Shell elongate-oval, with the beaks near the anterior 

 third, solid, closely regularly sculptured with fine radiating threads, the 

 interspaces wider, the threads a little stronger towards the ends of the 

 shell, concentric sculpture only of fine somewhat irregular incremental 

 lines; beaks rather elevated; shell moderately inflated, more or less 

 irregular from nestling among rocks, sculpture near the beaks quite faint; 

 hinge short, a spur from the lunular region extending over and past the 

 cardinal teeth behind the beaks; hinge normal; margins entire; pallial 

 sinus deep and rounded." Dall, 1900. 



Height, 9 mm.; width, 17 mm. ; diameter, 3.5 mm. 



Occurrence. — St. Mary's Formation. Cove Point. Choptank For- 

 mation. Jones Wharf, Calvert Cliffs (Burns and Harris). 



Collections. — Maryland Geological Survey, U. S. National Museum. 



