MARYLAND GEOLOGICAL SURVEY 287 



Description. — " Suboval, thin and fragile, with a fold on the posterior 

 submargin; umbo prominent; beaks nearly central, approximate; lunule 

 much elongated, lanceolate, slightly impressed." Conrad, 1832. 



Surface nearly smooth, teeth prominent, fosset large, pallial sinus 

 acutely rounded, distinguished from S. marylandica by having but one 

 elevated line on upper posterior slope. No specimens obtained were j)er- 

 fect enough to measure. 



Occurrence. — St. Mary's Formation. St. Mary's Eiver. Choptank 

 Formation. Governor Eun, Jones Wharf. Calvert Formation. 

 Chesapeake Beach. 



Collections. — Maryland Geological Survey, Johns Hopkins University. 



SpISULA (HEMIirACTRA) MARYLANDICA Dall. 



Plate LXIX, Fig. 11. 



Spisula {Hemimactra) marylandica Dall, 1898, Traus. Wagner Free Inst. Sci., vol. iii, 

 pt. iv, p. 897, pi. xxviii, flg. 5. 



Description. — " Shell large, suboval, thin, inflated, with a nearly 

 smooth surface, marked chiefly by incremental and obsolete radiating 

 lines; beaks high, subcentral, adjacent; anterior end excavated above, 

 rounded in front, posterior sloping to a bluntly pointed end behind; 

 anterior dorsal area smooth and deeply impressed; posterior area some- 

 what depressed, striated, flexuous, with three obscure, elevated lines, ex- 

 tending from the umbo to the margin outside of the area; base arcuate; 

 pallial sinus rather narrow, extending nearly to the middle of the shell, 

 bluntly pointed in front; hinge strong, with a large oblique chondrophore, 

 very short, smooth lateral laminae, and the anterior arm of the right car- 

 dinal tooth coalescent with the ventral lamina. 



"This fine species is at once differentiated from S. delumbis by its 

 more equilateral and inflated shell, and by having instead of only one 

 three elevated lines radiating backward from the beak." Dall, 1898. 



Length, 90 mm.; height, 67 mm.; diameter, 40 mm. (Dall). 



Occurrence. — St. Mary's Formation. St. Mary's Eiver. Choptank 

 Formation. Jones Wharf. Calvert Formation. Plum Point. 



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



