100 MOLLUSCA FROM THE CRAG. 



RissoA,* Freminville and Besmarest. 1814. 



TuRBOELLA. Leach, 1819. 

 Pyramis. Brown, 1827. 

 CiNGCLA. 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 subglolnilous, 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 sharji 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. Pliil. 

 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. Ilont. Tab. XI, fig. 1, a — b. 



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

 CiNGULA STRIATA. Flem. Brit. An. p. 307, 1828. 

 KissoA COMMUNIS. Forhes. Malac. Monen. p. 17, 1838. 



— STRIATA. jS. Wood. Catalogue 1842. 

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

 CiNGULA striata. Thorpe. Brit. Mar. Coucli. p. 178, fig. 99, 1844. 



R. Testa elongatd, turritu, subci/Iindraced, aince ohtuso ; anfractibus sex, convexis, 

 transversim striatis, et longitudinaliter sujjerne costatis ; aperturd ovatd, peristomate 

 integro, labro obliqiio, extiis incrassato, intus Itevigato. 



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. 



