64 MOLLUSCA. 



whose external base arc pedicles which support the eyes. They in- 

 habit the rivers of hot countries *. In the 



CALYPTRJBA, Lam. 



We observe a conical shell in the hollow of which is a little lamina 

 that projects inwards, resembling the commencement of a columella, 

 and that interposes itself between a fold of the abdominal sac. The 

 branchiae are composed of a range of numerous filaments, long and 

 slender, like hairs. 



In some of them this lamina adheres to the bottom of the cone, 

 being itself bent into a portion of a cone or of a tube, and descending 

 verticallyf. 



In others it is almost horizontal, and adheres to the sides of the 

 cone, which is marked above by a spiral line that establishes some 

 relation between their shell and that of a TrochusJ. 



SIPHON ARIA, Soiverby. 



The shell of the Siphonariae, which have been recently separated 

 from the Patellae, at the first glance seems very similar to a flattened 

 Patella, with radiating sulci; but its margin projects rather more 011 

 the right side, and it is excavated beneath by a slight furrow, which 

 terminates at this prominence of the margin, to which there is a 

 corresponding lateral hole in the mantle, for the introduction of 

 water into the branchial cavity placed on the back, that is closed on 

 every other point. The respiratory organ consist of a few small 

 lamellae, arranged in one transverse line on the roof of that cavity ; 

 the tentacula seem to be wanting, the head being merely furnished 

 with a narrow veil. 



There are some species, in which even this slight appearance of 

 the canal, in the shell, is effaced, resembling in toto that of a Patella, 

 except in its summit, which is behind ||. In the 



SIGARETUS, Adans. 



The shell is flattened, its aperture ample and round, and the spire 

 very moderate, its whorls rapidly enlarging and seen within, but 

 concealed during the life of the animal in the thickness of a fungous 

 shield, which projects considerably beyond it, as well as the foot, 

 and which is the true mantle. Before this mantle are an cmargina- 



* Patella neritonlea, List., 545 36, and Naturf., XIII, v, 1, 2 ; Pat. borbonica, 

 Bory Saint-Vincent, Voy. I, xxxvii, 2 ; and for the animal, Quoy and Gaym., Voy. 

 de Freycin., pi. 71, f. 3 6. 



-f- Patella equeslris, L., List., 546 38; Pat. sinensis, Ib., 39 ; Pat. trocJiiformis, 

 Martini, I, xiii, 135; Pat,, auricula, Chemn., X, clxviii, 1 628 29 ;Pat. plicafa, 

 Nat. Forsch., XVIII, 11, 12 ; Pal.striata, Ib., 13. 



J Patella contorta, Nat. Forsch., IX, iii, 34, VIII, 11 14 ; Pat. depressa, Ib., 

 xviii, ii, 11. 



Patella aiplio ; Siphonovia concinnu, Sowerb., Gen. of Shells, No. XXI. ; S. 

 erigua, Id., Ib. See Savigny, Descr. de 1'Eg., Zool. Gaster., pi. iii, f. 3, and Coq., 

 pi. i, f. 1. Some years ago M. Gray proposed a genus GADINIA, (Philos. Magaz., 

 April 1824) which is precisely the same as SIPHONARIA. 



|| Siphonaria t)"istensis t Sowerb., loc. cit. 



