202 SYSTEMATIC PALEONTOLOGY 



Length, 12 mm.; height, 6.5 mm. 



Occurrence. — Nanjemoy Foemation. Popes Creek, "Woodstock, 1 

 mile southeast of Piscataway, 2J to 3 miles above Popes Creek. 



Collections. — Maryland Geological Survej^, Philadelphia Academy of 

 Natural Sciences. 



Family NUCULIDAE. 



Genus NUCULA Lamarck. 



NucuLA ovuLA Lea. 

 Plate LVII, Fig. 6. 



Nucula ovula Lea, 1833, Contvib. to GeoL, p. 80, pL iii, fig. 59. 



Description. — " Shell ovate, oblique, inflated, very inequilateral, trans- 

 versely striate, longitudinally and very minutely ribbed; substance of 

 the shell thin; lunule large, not deeply impressed; beaks pointed, re- 

 curved; anterior series of teeth short, posterior series long; fosset nearly 

 direct; cavity of the shell deep; margin very minutely crenulate; nacre 

 pearly." Lea, 1833. 



Length, 11 mm.; height, 7.5 mm. 



Occurrence. — Aquia Formation. Upper Marlboro, Sheckel's Farm 

 near South Eiver. 



Collection. — Maryland Geological Survey. 



JSTucuLA potomacensis n. sp. 

 Plate LYII, Figs. 7, 7a, 8, 8a. 



■Nucula magnifica Clark, 189.5, Johns Hopkins Univ. Circ, vol. xv, p. 5. 

 Nucula magnifica Clark, 1896, Bull. 141, U. S. Geol. Survey, p. 82. 

 Not Nuciila magnifica Conrad. 



Description. — Shell small, thin, fragile; valves shallow; surface mark- 

 ed by strong radial striae which are stronger toward the periphery, and 

 along which the shell tends to fracture; margin strongly crenulated; 

 lines of growth faint and irregular, other concentric sculpture lacking; 

 interior with a silvery luster; beaks anteriorly situated; lunule indis- 

 tinct; chondrophore narrow, oblique; anterior teeth about fifteen, pos- 

 terior teeth about six. 



