208 PYRAMID ELLID^. 



Genus SYRNOLOPSIS, E. A. Smith, 1880. 



Shell subulate, smooth, imperforate ; aperture broacll}' sinuated 

 at the base, outer lip sinuous, slightlj^ thickened, furnished far 

 within with one or two promiiient lirse, columella with a distinct 

 plait. Operculum unknown. S. lacustris, Smith. Lake. Tanga- 

 nyika, E. Africa (fresh water). 



The systematic position of this group is very uncertain : being 

 lacustrine. Dr. Fischer has included it with doubt in the Hydro- 

 biime, but the characters of the shell (the apex is eroded) ap- 

 pear to me to be closer to the present family. 



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Genus NERIN^A, Defrance, 182.^. 



Shell elongated, many-whorled, nearly cylindrical; aperture 

 channeled and produced in front, with plications within the outer 

 lip and on the columella. About 150 species, Jurassic and Creta- 

 ceous. N. TRiNODOSA, d'Orb., Struct, and Syst. Conch., t. 68, f. 

 10; N. TRACHEA, Desh., Ibid. t. 68, f. 13. 



Section NERiNiEA (sensu stricto). 



Folds simple, two or three on the columella, one or two within 

 the outer lip ; axis solid or perforated. 



Section Nerinella, Sharpe, 1850. 



Columella solid, folds simple, one on the outer lip,, and one or 

 none on the columella. 



Section Trochalta, Sharpe, 1850. 



Columella perforated, with one fold, outer wall simple, or 

 thickened, or with one simple fold. 



Section Ptygmatis, Sharpe, 1850. 



Columella solid or perforated, usually with three folds ; outer 

 wall with one to three folds, some of them complicated in form. 



Subgenus Halloysta, Briart and Cornet, 1878. 

 Shell elongated, turriculated ; whorls numerous, axis widely 

 umbilicated ; aperture rounded or subquadrangular, columella 

 biplicate. 



N. biplicata, Br. et Corn. Struct, and Syst. Conch., t. 68, f. 14. 

 L. Eocene of 1/ons, Belgium. 



