148 MANUAL OF THE MOLLUSCA. 



Shell elongated, many- whirled ; whirls variously sculptured, and zoned 

 like pleurotomaria ; aperture slightly channelled in front ; outer lip deeply 

 notched. 



The murchisonise are characteristic fossils of the palseozoic rocks ; they have 

 been compared to elongated pleurotomarige, or to cerithia with notched aper- 

 tures ; the first suggestion is most probably correct. 



Fossil, 50 sp. L. silurian -Permian. N. America, Europe. 

 TROCHOTOMA, Lycett. 



Etym., trochus, and tome, a notch. 



Syn., ditremaria, D'Orb. 



Type, T. conuloides. PI. X., fig. 26. 



Shell trochiform, slightly concave beneath; whirls flat, spirally striated, 

 rounded at the outer angles ; lip with a single perforation near the margin. 



Fossil, 10 sp. Lias Coral Rag, Brit., Trance, &c. 



? CIKRUS, Sowerby. 



Etym., cirrus, a curl. 



Type, C. nodosus, Sby. Min. Con. t. 141 and 219. 



Shell sinistral, trochiform, base level ; last whirl enlarging rather more 

 rapidly, somewhat irregular. 



Fossil, 2 sp. Inf. oolite, Bath oolite. Brit., France. 



This genus was founded on a pleurotomaria, a euomphalus, and C. nodosus. 

 (r. Min. Con.) It is still doubtful what species may be referred to it. 



IANTHINA, Lam. Violet-snail. 



Etym., ianthina, violet-coloured. 



Type, helix ianthina L. (I. fragilis, Lam.) PL X., fig. 27- 



Shell thin, translucent, trochiform ; nucleus minute, ;Jstyliform, sinistral ; 

 whirls few, rather ventricose ; aperture four- sided ; columella tortuous ; lip 

 thin, notched at the outer angle. Base of the shell deep violet, spire nearl) 

 white. 



Animal: head large, muzzle-shaped, with a tentacle and eye -pedicel or 



* Fig. 89. Ianthina fragilis, Lam. (from Quoy and Gaimard). Atlantic, a raft 

 b egg capsules, c gills, d tentacles and eye-stalks. 



