PULMONARY GASTEEOPODS. 



415 



fringed in its circumference, and furnished with a horny operculum, 

 circular and regularly spiral. 



The family is divided into many sub -genera. Among the Trochi, 

 properly so called, we may notice Trochus niloticus (Fig. 219), T. vir- 

 gatus (Fig. 220), T. inermis (Fig. 221), and T. Cookii (Fig. 222). 



The genus Turbo are very generally diffused, being found on every 



Fig. 225. Turbo margaritaceus 

 (Linnaeus). 



Fig. 226. Turbo argyrostomus (Linnaeus). 



Fig. 227. Turbo marmoratus (Linnaeus), Fig. 228. Turbo undulatus (Chemnitz). 



shore, where they cling to rocks beaten by the waves. About fifty 

 species are known, some of them large shells, others very small. 

 Turbo margaritaceus (Fig. 225) is large, thick, and weighty, round- 

 bellied, and deeply furrowed ; in colour it is yellow, or rust-coloured, 

 marked by square brown spots. Turbo argyrostomus, the Silver- 

 mouthed Turbo (Fig. 226), is still larger, with protecting spines on the 



