MAItVI.WI) CI'OI.OGICAL SURVEY 181 



in;itci-i;il licliMiL^iiiu- l<> this i iii|i()rl;iiit species, it ajipeai's that tln' forms 

 figured and described by Kugcrs ami lleil|iiiii as distinct species are only 

 varieties of Conrad's C. almfonnis. Tim species is largely represented 

 in the lower portion of tlie Middle Atlantic Coast series, especially in 

 the Piscataway substago of the .\i|iiia foiinat inn. It is I'ai'ei' in llie Tas- 

 ])otansa subslagc. and here two distinct forms ai'e found, each dilfercnt 

 from the older forms. Tim specimens from the sandy beds along the 

 Potomac are small and very elongate, the average size being 40 x 20 ram. 

 The indnrated ledge at Upper Marlboro, Hardesty, Snnth Kivcr bridge, 

 and l\ol|ilis T>aiiding contains a very large foi'ni at the olher end of tlie 

 alacformis series. This reaches the size and proportions of 90 x GO mm., 

 but a single specimen from South Eiver, which may however belong to 

 another species, attains the size of 95 x 80 mm. The larger elongate 

 forms a|iproacli the several Miocene species in size and outline. The 

 specimens from the various beds of the Piscataway substage vary greatly 

 in size and form and connect the Paspotansa varieties with each other 

 and almost connect them with C. aquiana. C. palmula Conrad prob- 

 ably belongs in this series. 



Length, 40 to 90 mm.; height, 20 to 60 mm. 



Occurrence. — Aquia Formatiox. Paspotansa Creek, 2 miles belov 

 Potomac Creek, Potomac Creek, 1 mile southeast of Mason Springs, Clif 

 ton. Beach, Glymont, Mattawoman Creek, Liverpool Point, Wades Bay. 

 Aquia Creek, 1 mile northeast of Piscataway, Brooks Estate near Seat 

 Pleasant, Port Washington, Upper Marlboro, 3 miles west of Leeland on 

 Western Branch, West of CoUington, between Buena Vista and Colling- 

 ton, SheckeFs Farm near South Kiver, Eolphs Landing. 



Collections. — Maryland Geological Survey, Johns Hopkins University, 

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



Ceassatellites aqitiaxa (Clark). 

 Plate XIJI, Figs. 1, 2a, 2b. 



Crasaatella aquiana Clark, 1895, Johns Hopkins Univ. Circ, vol. xv, p. 5. 

 Crassatella aquiana Clark, 1896, Bull. 141, U. S. Geol. Survey, p. 82, pi. xxvi, figs. 

 2a-2c. 



Description. — ''Shell moderately large, attenuated posteriorly; surface 

 with a few broad, shallow, concentric furrows, indicating periods of 



