134 MANUAL OF THE MOLLUSCA. 



with a rudimentary siphonal fold ; foot obtusely triangular, with a fold (men- 

 turn) in front. Lingual dentition nearly as in bulla ; teeth ; uncini nume- 

 rous, simple; sexes distinct; predacious? Range fi-om low water to 80 

 fathoms. The animal exudes a purple fluid when molested. 



Bistr., nearly 100 sp. Mostly tropical. Greenland, Norway, Brit., 

 Medit., W. Indies, China, Australia, Pacific, W. America. 



Fossil, nearly 100 sp. Coral-rag—. Brit., N. America, Chile, India. 



FAMILY VI. Lttorinid.e 



Shell spiral, turbinated or depressed, never peai'ly ; apertm-e rounded ; 

 peristome entire ; operculum horny, pauci-sinral. 



A7dmal vdth a muzzle-shaped head, and eyes sessUe at the outer bases of 

 the tentacles ; tongue long, ai'med with a median series of broad, hooked teeth, 

 and 3 oblong', hooked uncini. Branchial plume single. Foot with a linear 

 duplication in front, and a groove along the sole. ]\Iantle with a rudimentary 

 siphonal canal ; operc. lobe appendaged. 



The species inhabit the sea, or brackish water, and are mostly literal, feed- 

 ing on algae. 



LiTORiNA, Ferussac. Periwinkle. 



Efpn., litns, the sea-shore. 



Tijpe, L. litorea, PI. IX., fig. 10. 



Shell turbinated, thick, pointed, few-whiiied ; aperture 

 rounded, outer lip acute, columeUa rather flattened, imperforate, ^ 

 operculum pauci-spiral, fig. 81. Lingual teeth hooked and tri- .(^ 

 lobed ; uncini hooked and dentated. _ \^^ j 



Distr., 40 sp. The periwinldes are found on the sea-shore, in X^i J 

 aU pai-ts of the world. In the Baltic they Hve within the in- Fig. 81. 

 fluence of fresh- water, and frequently become distorted ; similar monstrosities 

 are found in the Norwich crag. 



The common sp. {L. litorea) is oviparous ; it inhabits the lowest zones of 

 sea-weed between tide-marks. An aUied sp. (L. rudis) frequents a higher 

 reoion, where it is scai'cely reached by the tide ; it is \dviparous, and the 

 Young'have a hard sheU before their birth, in consequence of which the species 

 is not eaten. The tongue of the periwinkle is two inches long ; its foot is 

 dixided by a longitudinal line, and in walking the sides advance alternately. 

 The peiiwinkle and trochus are the food of the thrush, in the Hebrides, dming 



winter. 



Fossil, 10 sp? Miocene—. Brit., &c. It is probable that a large propor- 

 tion of the oolite and cretaceous shells referred to turbo, belong to this genus, 

 and especially to the section tectaria. 



Sub-genera. Tectaria, Cuvier, 1817 (= PagodeUa, Sw.) L. pagodus, 

 PI. IX., fig. 11. Shell mmicated or granulated ; sometimes with an umbilical 



