298 PYKAMIDELLID^E. 



Genus SYRXOLOPSIS, E.. A. Smith, 1880. 



Shell subulate, smooth, imperforate ; aperture broadly sinuated 

 at the base, outer lip sinuous, slightly thickened, furnished far 

 within with one or two prominent lirae, 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- 

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

 pear to me to be closer to the present family. 



* * * 

 Genus NERIXJBA, Defrance, 1825. 



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 NERIN^EA (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 TROCHALIA, Sharpe, 1850. 



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

 thickened, or with one simple fold. 



Section PTYGMATTS, 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. BIPLTCATA, Br. et Corn. Struct, and Syst. Conch., t. 68, f. 14. 

 L. Eocene of Mons, Belgium. 



