148 



MANUAL OF THE MOLLUSCA. 





Shell elongated, many-wliirled ; wliirls variously sculptured, and zoned 

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

 notched. 



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

 been compared to elongated pleurotomarise, 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. 



Etpn., trochus, and tome, a notch. :;• 



Syn., ditremaria, D'Orb. 



Ty])e, 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., France, &c. 



? Cirrus, Sowerby. 



Etym., cirnis, a curl. 



Ty2)e, C. nodosus, Sby. Min. Con. t. 141 and 219. 



Shell sinistral, trochiform, base level ; last w^hirl enlarging rather more 

 rapidly, somewhat irregular. 



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



This genus was founded on a plem'otomaria, a euomphalus, and C. nodosus. 

 (v. Min. Con.) It is stiU doubtful what species may be referred to it. 



Fig. 89.* 



Ianthina, Lam. Violet-snail. 



Etym., ianthina, violet-coloured. 



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



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

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

 thin, notched at the outer angle. Base of the sheU deep violet, spire nearly 

 white. 



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



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

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



