186 SYSTEMATIC PALEONTOLOGY 



ton Beach, Wades Bay, Aqnia Creek (Zones 2 and 3), Potomac Creek, 2 

 miles below Potomac Creek, Glymont, 1 mile southeast of Mason Springs, 

 Upper Marlboro, Fort Washington, ]\Iouth of Paspotansa Creek. 



Collections. — Maryland Geological Survey, Johns Hopkins University, 

 U. S. National Museum, Philadelphia Academy of Natural Sciences. 



Modiolus maeylandicus n. sp. 

 Plate XLIII, Fig. 6. 



Description. — Shell thin and fragile; beaks elevated, strongly incurved, 

 and situated far back of the anterior extremity; surface marked by strong 

 lines of growth and faint radiating lines, developing into strong radial 

 cracks. 



One specimen only, and that showing parts of both valves, has been 

 found; while another that may belong to this species, although it shows 

 some quite different characteristics, was also obtained. 



Length (of fragment), 20 mm.; width, 10 mm. 



Occurrence. — Nanjemoy Fokmation. Woodstock. 



Collection. — Maryland Geological Survey. 



Genus LITHOPHAGA Bolten. 

 LiTHOPHAGA MAEYLANDICA n. Sp. 



Plate XLIII, Fig. 7. 



Solemya petricoloides Clark, 1895, Johns Hopkins Univ. Circ, voL xv, p. 5. 

 Solemya petricoloides Clark, 1896, Bull. 141, U. S. Geol. Survey, p. 74. 

 Not By ssomy a petricoloides Lea. 



Description. — " Shell elongated, very inequilateral, slightly gaping, 

 thin; surface nearly smooth with fine lines of growth; umbones very 

 posteriorly situated; hinge edentulous; pallial line obscure." Clark, 

 1896. 



Our specimens differ from petricoloides in having the beaks nearly 

 terminal. 



Length, 11 mm.; width, 4.5 mm. 



Occurrence. — Aquia Foemation. Clifton Beach. 



Collections. — Maryland Geological Survey, Johns Hopkins University. 



