MAUVLAXD GEOLOGICAL Sl'RVFY 131 



subacute tubercles, which are also distinct on the spire: transversely 

 striated at base: two folds on the columella." Conrad, 1833. 



The ]\IaiTl;uid spcfinions are principally of the hionifi/i type, but tlir 

 iKiriiml I'Dnii ucciifs with it at most localities. 



Length, iis mm.; widtli, 2-) mm. 



Occurrence. — Naxjkmoy Formation'. Wood.'^tock, Popes Creek, West 

 of Port Tobacco. Aquia Formatiox. Potomac Creek, 2 miles below 

 Potomac Creek, 1 mile northeast of Piscataway, 1 mile southeast of 

 Mason Springs, Aquia Creek. 



Collections. — ^Maryland Geological Survey, Johns Hopkins University, 

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



VOLUTILITHES Sp. 



Plate XXI, Figs. 6, 6a. 



Volutilithes sp. Clark, 1895, Johns Hoplvins Univ. Circ, voL xv, p. 4. 



Volutilithes sp. Clark, 1896, Bull. 141, U. S. Geol. Survey, p. 05, pi. x, figs. 2a, 2b. 



A fine cast of a large species of Volutilithes was obtained from the in- 

 durated ledge. Zone 3, at the Aquia Creek bluffs, and a very imperfect 

 specimen from Potomac Creek. It is unlike any of the species of Volu- 

 tilitlies hitherto described, but from the fact that the shell substance is 

 almost lacking no attempt will be made to give a full description. It 

 has a somewhat compressed form, due to pressure. 



The shell substance is extremely thin, and the surface is marked only 

 by lines of growth. The tubercles are obtuse and distant, and the spire 

 small. 



Length, 75 mm.; width, 53 mm. 



Occurrence. — Aquia Foematiox. Aquia Creek, Potomac Creek. 



Collections. — Maryland Geological Survey, Johns Hopkins University. 



Genus CARICELLA Conrad. 



Caeicella pyeuloides (?) (Conrad). 



Plate XXI, Figs. 7, 8. 



TiirbineUa pi/ridoicJes Conrad, 1S33, Fossil Shells of the Tertian.-, Xo. 2, p. 24, pi. x, 



fig. 1. 

 (?) Caricella sp. Clark, 1895, Johns Hopkins Univ. Circ, vol.''xv, p. 4. 

 (?) Caricella sp. Clark, 1896, Bull. 141, U. S. Geol. Survey, p. 66, pi. xi, tig. 1. 



