Order G. 



GASTEllOPODA PECTIXIBRANCHIATA. 



357 



foot, pointed beliiiul, wicleued in front, wncreit is marked witli two deep emarg-inations. The eyes are on the sides 

 of tlie tentiicula, near the base. 'I'lieie is no veil nor operculum. (MM Keynaud, and Quoy and Gaymard have 

 observed that, under certain circumstances, the hinder part of tlie foot is spontaneously amputated.) AVe recognize 

 the Purpura, Urus;., by its ilattened columella, pointed at the base, and foiining there, Viith the outer lip, a canal 

 e.Kcavated in the shell, but not projecting. The species were scattered among' the Buccina and Murices by Lin- 

 naeus. Their snail is like that of Buccinum as now restricted. Some shells similar to Pu)pi)ra, but in which we 

 notice a spine on the outer margin of the canal, form the geims Licorna, Montf. (Monoceros, Lam.) Others in 

 which the columella, or at least tlie lip, is garnished, in the full-grown shell, with teeth tliat narrow the mouth, 



las al.-o llif gesiera-1 



Fit;. ISO.— Cuucholepas peruviaaus. 





constitute the iS7«^ra of the former, and the liiciuula of Lamarck. Tlie Concholcpas, L:.u 



characters of the Purpura, but the aperture is so 



enormously large and the spire so inconsiderable, 



that the shell has the aspect of a Capulus, or of one 



of the valves of an Area. The emargination of the 



mouth has a small tooth on each side of it. The ani- 

 mal resembles that of Buccinum, excepting in the 



foot, which is enormous in width and in thickness, 



and which is attached to the shell by a muscle in 



form of a horse-shoe, as in Capulus. There is a thin, 



narrow, liorny operculum. A species from Peru 



(Buccinum concholepas, Brug.) is the only one known. 



Cassis, Brug. — Shell oblong; the aperture oblong or 

 narrow; the columella covered with a plate as in 

 Nassa, and that plate grooved transversely as well as 

 the outer lip : the emargination ends in a short canal, 

 which is folded and turned up backwards, and to the 

 left. There are often varices. [The shells are called 

 Helmets by English collectors, and are in general 

 remarkable on account of their great size.] The 

 animal resembles that of Buccinum, but its horny 

 operculum is toothed, that it may pass between the 

 grooves of the outer lip. Some have the varix of this 

 lip toothed externally near the emargination ; and 

 others have it plain. The Morio, Montf. (Cassidaria, 

 Lam.) are .separated from the Cassis because their 

 canal is less abruptly curved back ; and they lead 

 us to certain of the Murices. The animal resembles 

 a Buccinum also, but its foot is more developed. 

 \Oniscia, Sowerby, is sufficiently distinguished 

 from Cassidaria by its granulated inner lip, its very 

 short, scarcely reflected canal, and its very singular 



general form, which is oblong or subcylindrical, with an obtuse 

 apex. Strombus oniscus, Linn., is the type of the genus.] Terehra, 

 Brug., have the mouth, the emargination, and the columella of 

 Buccinnm, but their spire is drawn out so as to be turriculated or 

 subulate. [The sjiecics are numerous and beautiful.] The Suhulir, 

 Blainv., is distinguished by some difference in the animal, and by 

 the existence of an operculum. 



The Ceritiiium, Brug., — 

 Dismembered with good reason from the Murex of Linnceus, 

 Fig. i82.-cassuiaria cciiinophora. havc a shcll with a tumculated splre, an oval aperture, and 



a short but distinct canal 

 curved to the left and back- 

 wards. There is a veil on 

 the head of the animal, two 

 distant tentacula, having 

 the eyes at the side, and 

 a round, horny operculum. 

 Many of them are found in a fossil state. 



M. Brongniart has separated from Cerithium the Poianiides, which, with the same form of shell, have a very 

 short, scarcely emarginate canal, no sinus or gutter near the top of the right lip, and the exterior lip dilated. They 

 live in rivers, or at least at their mouths ; and some of them are fossil in formations wiiere there are no other 

 than land or freshwater species. 



Fig. ISI.— C-issis tuberosa. 



Fig. 183.— Ccrithcum. 



