250 MANtJAL OF THE MOLLUSCA. 



ScALAEiA, Lam. Wentle-trap. 



Etymology, scalaris, like a ladder. 



Type, S. pretiosa, PI. IX., Fig. 9. (= T. scalaris, L.) 



Shell mostly pure white and lustrous ; turreted ; many- 

 whorled; whorls round, sometimes separate, ornamented with 

 numerous transverse ribs ; aperture round ; peristome con- 

 tinuous; operculum horny, few-whorled. 



Animal with a retractile proboscis -like mouth ; tentacles 

 close together, long and pointed, with the eyes near their outer 

 bases ; mantle-margin simple, with a rudimentary siphonal 

 fold ; foot obtusely triangular, with a fold (inentum) in front. 

 Lingual dentition nearly as in bulla ; teeth ; uncini nume- 

 rous, simple ; sexes distinct ; predacious ? Eange from low 

 water to 80 fathoms. The animal exudes a purple fluid when 

 molested. 



Distribution, 104 species. Mostly tropical. Greenland, 

 Norway, Britain, Mediterranean, West Indies, China, Australia, 

 Pacific, West America. 



Fossil, nearly 100 species. Coral-rag — . Britain, North 

 America, Chili, India. 



Family VI. — LiTTORmiDiE. 



Shell spiral, turbinated or depressed, never pearly ; aperture 

 rounded ; peristome entire ; operculum horny, pauci-spiral. 



Animal with a mu2zle-shaped head, and eyes sessile at the 

 outer bases of the tentacles ; tongue long, armed 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. Mantle with a rudimentary 

 siphonal canal ; operculum lobe appendaged. 



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

 littoral, feeding on algse. 



LlTTORiNA, Ferussac. Periwinkle. 



Etymology, littoralis, belonging to the sea-shore. 

 Type, L. littorea, PL IX., Fig. 10, 

 Shdl turbinated, thick, pointed, few-whorled; 

 aperture rounded, outer lip acute, columella rather 

 flattened, imperforate, operculum pauci-spiral, Fig. 

 103. Lingual teeth hooked and trilobed ; uncini 

 Fig 103. hooked anddentated (Fig. 104). 

 Distribution, 131 species. The periwinkles are found on the 

 sea hore in all parts of the world. In the Baltic they live 



