PLEUROTOMA. 



the canal rather shorter than the spire, the upper part of 

 each volution thickened, with a groove beneath it, and the 

 notch in the outer lip at the lower edge of the groove; 

 this is one of Lamarck's Clavatulee ; fourth, with the canal 

 shorter than the spire and the upper edge of the volutions 

 muricated with strong spines, such is PI. muricata, Lam.; 

 fifth, with the aperture as long as the spire, and the canal 

 not distinguished from the aperture by a contraction of 

 the body of the shell, this leads to Conus ; sixth, having 

 the aperture and canal much shorter than the spire, and 

 the outer lip more or less expanded with a slight notch 

 near its lower end, leading to Strombus. We have thought 

 it advisable to illustrate this subject by a representation 

 of one of each of these variations. 



The recent Pleurotomae, although not remarkably 

 numerous, appear to be spread over the coasts of all parts 

 of the world, the finest species, nevertheless, belong to 

 tropical climates; the fossil species, which are very nume- 

 rous, principally abound in tertiary beds, they are found 

 in great numbers in the Calcaire grossier, in the London 

 Clay, in the contemporary beds near Bordeaux, and in 

 the Appennines. Some very beautiful species are repre- 

 sented by Brocchi in his work on the fossil shells of the 

 subappennine beds. 



Shell fusiform, turrited, aperture oval, with a more 

 or less elongated canal at the base ; outer lip with a notch 

 near the suture ; operculum horny, acuminated and having 

 its nucleus at the lower end : the operculum resembles 

 that of Fasciolaria and Strombus, and some species have 

 a thin epidermis, which appears, however, to be very 

 deciduous. In several species there is a very narrow, but 

 deep spiral groove just below the suture, which it is 

 extremely difficult to distinguish from the suture itself, 

 except at the edge of the outer lip; one of these remark- 

 able species we have named PI. Cryptorrhaphe and have 

 given a description of it in the Tankerville Catalogue, 

 appendix p. xiv. 



It is to be observed that Lamarck's PI. buccinoides 

 belongs to his family of MelanienSy and we have a species, 

 with whose locality we are unacquainted, but which we 

 suppose to be a freshwater shell, in whose peculiar form 

 the general characters of Pleurotoma are well marked, 

 which nevertheless has the epidermis of the Blelaniens and 

 like them is decollated. 



