200 SYSTEMATIC PALEOXTOLOGT 



the apex, except near the eud where it is some^yhat angulated." Con- 

 rad, 18^8. 



This very distinct species has been found only in and immediately 

 above the indurated ledge at Upper Marlboro and South River bridge. 

 It is rare in the indurated ledge but abundant in the shell bed imme- 

 diately above it. The type which came from Upper Marlboro is still in 

 the collection of the Philadelphia Academy of ISTaturah Sciences. 



Length, 15 mm.; height, 9 mm. 



Occurrence. — Aqtjia Foematiox. Upper Marlboro, Sheckel's Farm 

 near South Eiver. 



Collections. — Maryland Geological Survey, Philadelphia Academy of 

 Natural Sciences. 



Leda paeilis vae. 

 Plate LYII, Fig. 3. 



Leda impvocera Clark, Bull. 141, U. S. Geol. Survey, pi. sxviii, tig. \e. 



This form is a connecting link between L. cliftonensis and L. parilis 

 and might be the descendant of either. It is less globose and has 

 smaller, more numerous folds than L. parilis; and is somewhat more 

 elevated than L. cliftonensis with smaller, more closely-set folds. 



Length, 11 mm.; width, 6.5 mm. 



Occurrence. — ISTan'jemoy Foematiox. Hills Bridge, Woodstock. 



Collections. — Maryland Geological Survey, Johns Hopkins University. 



Leda potomacexsis n. sp. 

 Plate LVI, Figs. 9, 10. 



{?) Xiiculana protexla Conrad, 1865, Amer. Jour. Conch., vol. i, p. 147, pi. xi, fig. 6. 



(In part.) 

 Leda protexla Clark, 189.5, Johns Hopkins Univ. Circ, vol. xv, p. 5. 

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



Description. — "Shell large, transverse, elongate, anterior side round- 

 ed, posterior somewhat longer, attenuated, terminating in an obtuse 

 beak; surface with numerous concentric striations somewhat interfered 

 with on the rostrated portion of the posterior side, where the riblets 

 become more lamellated and wavy and at times even disappear." Clark, 

 1896. 



