100 MOLLUSCA FROM THE CRAG. 



Rissoa,* Freminville and Desmarest, 1814. 

 Turboella. Leach, 1819. 

 Pyrahis. Brown, 1827. 

 Cingula. Flem. 1828. 

 Cyclostrema. Id. 

 Loxostoma. Bivona, 1838. 



Gen. Char. Shell small, elongato-ovate, or turriculate, with generally an elevated 

 spire and acute apex, sometimes short and ovate, or subglobulous, smooth, striated, 

 or costated ; aperture suborbicular or ovate, acuminated at the upper part ; 

 peristome generally thickened and reflected, slightly intercepted at the base of the 

 columella by an incipient notch ; outer lip simple and sharp, or thickened and 

 dentated within. Operculum corneous, closing the aperture. 



This genus contains a large number of species, all of a small size, and shells are 

 included, with different forms of aperture, which, when the animals are better 

 known, may probably require to be separated ; some have a circular, continuous, 

 and thickened peristome, while others are subcanaliculated or slightly emarginate ; 

 many of them are strong and opaque shells, with thick and elevated costse, while 

 others are smooth, glossy, and vitreous, with a sharp and simple outer lip. The 

 name of Rissoa was proposed in 1814 by the above authors, who described several 

 species in the ' Bull, de la Soc. Phil, de Paris.' This genus appears first in the 

 Great Oolite, four species from which formation are described in ' Min. Conch=' 

 Many of the known recent species are inhabitants of shallow water. 



M. d'Orbigny has separated those species which have an indication of a sinus at 

 the upper as well as at the lower part of the aperture, and has united them into a 

 genus, under the name Rissoina. 



1. Rissoa striata. Mont. Tab. XI, fig. 1, a — b. 



Turbo striatus. Mont. Test. Brit. p. 312, 1803. 

 ClNfitiLA striata. Flem. Brit. An. p. 307, 1828. 

 Rissoa communis. Forbes. Malac. Monen. p. 17, 1838. 



— striata. S. Wood. Catalogue 1842. 

 Not. Rissoa striata. Phil. En. Moll. Sic. vol. i, t. 10, fig. 8. 

 Cinodla striata. Thorpe. Brit. Mar. Conch, p. 178, fig. 99, 1844. 



B. Testa elongate!, lurritd, subcylindraced, apice obtuso ; anfractibus sex, convexis, 

 transversim striatis, et longitudinaliter superne costalis ; aperturd ovatd, peristomate 

 integro, labro obliquo, extus incrassato, intus Icevigato. 



Shell small, elongate, subcylindrical, with an obtuse apex ; whorls six, convex, 

 transversely striated, and longitudinally costated upon the upper part of the volution, 



* Etym. After the name of M. Risso. 



