132 SYSTEMATIC PALEOXTOLOGY 



Description. — "Pyriforni, ventricose, smooth; with obscure spiral 

 striae on the inferior half of the body whorl; spire rery short; apex 

 slightly mammillated; columella with -i distant oblique plaits." Con- 

 rad, 1833. 



The specimens which are referred to this species consist of the cast 

 and the broken shell which are figured, and a still more imperfect cast. 

 It is not certain that they belong to the same species, or that any of 

 them belong to the species to which they are here referred. If they do 

 not belong here they probably represent one or more undescribed species. 



Length, 55 mm.; width, 23 mm. 



Occurrence. — Aquia Foemation. Potomac Creek, Aquia Creek, Liv- 

 erpool Point. 



Collections. — Maryland Geological Survey, Johns IIoj)kins L^niversity. 



Genus MITRA Lamarck. 

 MiTEA MAEYLANDICA Clark. 



Plate XXI, Figs. 9, 9a. 



Mitra marylandica Clark, 1895, Johns Hopkins Univ. Circ, vol. xv, p. 4. 

 Mitra marylandica Clark, 1896, Bull. 141, U. S. Geol. Survey, p. 66, pi. xi, figs. 4«, 

 46 (not 3). 



Description. — "Shell small, rather thick, with six (?) whorls; surface 

 with numerous, thickly-set spiral threads, crossed by fine wavy lines, 

 giving a finely reticulated appearance; spine moderately high; suture 

 distinct, appressed; shoulder not prominent; aperture elongated; col- 

 umella nearly straight, with three plaits." Clark, 1896. 



The essential character which distinguishes this species from the fol- 

 lowing is the lack of ribbing. 



Length, 21 mm.; width, 7 mm. 



Occurrence. — Aquia Foematiox. Pomonkey Keck. 



Collection. — L^. S. National Museum. 



Mitea pomoxkexsis n. sp. 

 Plate XXI, Figs. 10, 10a. 



Mitra up. Clark, 189.5, Johns Hopkins Univ. Circ, vol. xv, p. 4. 



Mitra Kp. Clark, 1896, Bull. 141, U. S. Geol. Survey, \\ 66, pi. xi, figs. ;)</, Sb. 



Description. — Shell larger than M. marylandica; whorls strongly con- 

 vex, and with a somewhat angulated shoulder slightly above the middle; 



