TROCHUS. 133 



The genera of British TrochidcB are— 

 I. Trochus. — The animal has a large head, ending in a 

 rather truncated proboscis : it has two rather long 

 tentacles, with a short eye-bearing peduncle at the 

 base of each ; a pair of lappets between the tentacles, 

 and another scalloped lappet on each side, behind them, 

 on the body, which has three cirrhi on each side. Shell 

 pyramidal ; operculum horny. The species are — 



T. zizijjjhirms, or conulus : the sides of the shell, unless 

 white, are coloured with brownish flames ; the spiral 

 lines are sometimes mounted into ridges, sometimes 

 some of them slightly beaded; the figure is very 

 conical, and the inner side of the aperture has no hol- 

 low behind it. Animal mottled with bright reddish- 

 brown. 



T. conulus: shell more strictly conical, with the whorls 

 straight and smoot/i ; colour arranged in rows of lines 

 and spots. 



T. alahastrum : shell white, with three spiral ridges on each 

 whorl of the spire, the top of them beaded. 



T. granulatus: the shell is rather rounded and swelled, and 

 has spiral rows of beads on the whorls. The animal is 

 very large in proportion to the shell, the foot being 



