CREITHIID^E. 119 



? Genus EXELTSSA, Piette, 1860. 



Shell siuall, elongated, subcylindrical, somewhat pupiform, many 

 whorled, longitudinally costate, tuberculate, or spinose, last whorl 

 tending to sej^arate from the axis, contracted at the base ; aperture 

 orbicular, entire, the lip produced and slightly thickened, colu- 

 mella solid. Kilvertia, Lycett, 1863, is a synonym. 



E. FORMOSA, Lycett (Stnirt. and %f. Coneh., t. 69, f. 62). Oolite, 

 England. A doubtful member of the family. 



? Genus PTEROSTOMA, Deshayes, 1861. 



Shell small, turreted, subcylindrical, Avhorls numerous, with lon- 

 gitudinal tubercular ril)s, and sj)iral striiB ; aperture circular, entire, 

 margin dilated, exteriorly thickened. 



P. TUBA, Desh. (jStrtict. and Syst. Conch., t. 72, f. 42). Eocene, 

 Paris basin. 



Genus CERITHIOPSIS, Forbes and Hanley, 1853. 



Small, imjierforate, more or less cylindrical, narrow, tuberculate, 

 not varicose ; whorls numerous, the last narrower in proportion ; 

 aperture small, with a short, truncate, nearly straight canal. Oper- 

 culum suboval, paucispiral, with sublateral, internal nucleus. 

 Animal with a narrow foot, subtruncated in front and attenuated 

 behind, with a longitudinal sulcus on the sole ; tentacles cylindrical, 

 the eyes sessile at their base ; opercular lobe simple, well developed. 



Radula with an oval central tooth, its margin dentate, a large, 

 bicuspid lateral tooth, and unicuspid laterals with smooth margin. 

 Mostly occurring in northern and temperate seas. Fossil, Cre- 

 taceous. 



C. TUBERCULARIS, Mont. 



Section MetaxIa, Monts., 1884. 



Base truncate, basal area not cingulate and concave, canal open, 

 incipient. C. rugulosa, Sowb. 



Section Seila, A. Ad., 1861. 



Shell with simple spiral ribs. C. dextroversa. Ad. and Reeve. 

 Cinctella, Monts., is a synonym. 



Section Lovexella, O. Sar.s., 1878, 



Shell subulate ; whorls numerous, cancellated, aperture termi- 

 nating in a short, distinct, reflected canal. C. metula, Loven. 

 Northern Seas. 



Cerithiella, Verrill, 1882, is a synonym. 



