TRUNCATELLlDiE. 211 



Lanistes, Montfort. 



Bistr. — East Africa. L. Bolteniana, Chemn. (Ixxiv, 19). 



Shell sinistral, depressed ; umbilicated ; peristome simple, 

 sharp. Operculum horny. 



MELADOMUS, Swainson. Shell sinistral, oval-conic, not umbili- 

 cated. Africa. L.olivacea, Sowb. (Ixxiv, 20). 



Marisa, Gray. 



Syn. — Ceratodes, Guilding. 



Biatr. — -A few species. So. America, West Indies. M. cornu- 

 arietis, Linn. (Ixxiv, 21). M. Chiquitensis, d'Orb. (Ixxiv, 23). 



Shell flattened or planorbiform, spire depressed or very 

 slightly elevated ; widely umbilicated ; aperture expanded. 

 Operculum horny. 



Family TRUNCATELLID^. 



Shell subcjdindrical or turbinate, with elevated spire, apex 

 obtuse or truncate ; aperture oval, entire, peristome continuous. 

 Operculum subspiral. 



Animal with short, diverging triangular tentacles, and eyes 

 at their bases. Amphibious, inhabiting usually margins of 

 streams, salt marshes, damp places, etc. The relationship of 

 these mollusks with the Rissoids and Assiminise is very close, 

 so that they may be considered as terrestial Rissoidse ; on the 

 other hand, they connect with the typical operculated land-shells, 

 the Cyclostomse. 



Truncatella, Risso. 



Looping snail. Syn. — Choristoma, Crist, and Jan. Erpeto- 

 metra, Lowe. 



Bistr. — 62 sp. World-wide, mostly tropical. Fossil. Eocene; 

 Paris basin. T. truncatula, Drap. (Ixxv, 24). 



Shell minute, C3dindrical, truncated ; whorls striated trans- 

 versely ; aperture oval, entire ; peristome continuous. Opercu- 

 lum corneous, subspiral. 



Animal with short, diverging, triangular tentacles ; eyes 

 centrally behind ; head bilobed ; foot short, rounded at each 

 end. — Forbes. 



The Truncatellae are found on stones and sea-weeds between 

 tide-marks, and survive many weeks out of the water. — Lowe. 

 They walk by contracting the space between their lips and foot, 

 like the geometric caterpillars. — Gray. They are found semi- 

 fossil along with the human skeletons in the modern limestone 

 of Guadaloupe. 



taheitea., H. and A. Ad. Operculum calcareous, radiately 

 lamellate. Aperture usually more or less separated from the 

 preceding whorl. Polynesia. T. Vitiana, Pease. Viti Isles. 



