FAMILY 4. IANTHINEA. 143 
Examples. 
BISCCIV. Fig al: 
Nartica CANRENA, Lamarck, Anim. sans vert., new edit., vol. vii. p. 633. 
Chemnitz, Conch., vol. v. pl. 186. f. 1860 and 1861. 
Nerita canrena, Linnzus. 
Pl. CCIV. Fig. 2. 
Natica MAMILLA, Lamarck, Anim. sans vert., new edit., vol. viii. p. 630. 
Chemnitz, Conch., vol. v. pl. 189. f. 1928 to 1931. 
Nerita mamilla, Linneus. 
Polinices ——-—? De Monttford. 
Pl. CCIV. Fig. 3. (fossil.) 
Natica cepacea, Lamarck, Anim. sans vert., new edit., vol. vili. p. 653. 
Ann. du Mus., vol. v. p. 96; and vol. viii. pl. 62. f.5.a,b. Deshayes, 
Désc. Cog. Foss. de Paris, vol. ii. p. 168. pl. 22. f. 5 and 6. 
Pl. CCIV. Fig. 4. (a fossil shell from Piacenza.) 
Family 4. IANTHINEA. 
Animal vesiculis cartilagineis plurimis, disco affixis, super aquas jugiter 
latum. 
The Ianthinea, though few in number, differ materially from other 
mollusks both in their organization and habits ; their shell is exceedingly 
light and fragile, but they are nevertheless marine. The peculiarity of 
these animals consists in having the ventral part of the pedal disc furnished 
with a number of cartilaginous vesicles, which cause them to float upon 
the surface of the ocean, and they have also a small aving-like appendage 
attached to each side of the body. It has been supposed by some authors 
that the Janthinea have the power of contracting or inflating these air- 
