% GASTEROPODA, 271 
rocks; they have been compared to elongated plewrotomarie, 
or to cerithia with notched apertures; the first suggestion is 
most probably correct. 
Fossil, 50 species. L. Silurian—Permian. North America, 
Europe. 
TrocHOTOMA, Lycett. 
Etymology, Trochus, and tome, a notch. 
Synonym, Ditremaria, D’Orbigny. 
Type, T. conuloides, Pl. X., Fig. 26. 
Shell trochiform, slightly concave beneath; whorls flat, 
spirally striated, rounded at the outer angles; lip with a single 
perforation near the margin. 
Fossil, 10 species. Lias—Coral Rag. Britain, France, &c. 
? CIRRUS, Sowerby. 
Etymology, cirrus, a curl. 
Type, C. nodosus, Sby. Min. Con. t. 141 and 219. 
Shell sinistral, trochiform, base level; last whorl enlarging 
rather more rapidly, somewhat irregular. 
Fossil, 2 species. Inf. oolite, Bath oolite. Britain, France. 
This genus was founded on a plewrotomaria, a euomphalus, 
and ©. nodosus. (vy. Min. Con.) I¢ is still doubtful what 
species may be referred to it. 
Fig. 117.* 
TANTHINA, Lam. Violet-snail. 
Etymology, ianthina, violet-coloured. 
Type, helix ianthina, L. (I. fragilis, Lam.) Pl. X., Fig. 27. 
Shell thin, translucent, trochiform; nucleus minute, styliform; 
sinistral; whorls few, rather ventricose; aperture four-sided ; 
columella tortuous; lip thin, notched at the outer angle. Base 
of the shell deep violet, spire nearly white. 
Animal head large, muzzle-shaped, with a tentacle and eye- 
* Fig. 117. Janthina fragilis, Lam. (from Quoy and Gaimard), Atlantic. a, raft, 
6, egg capsules; c, gills; d, tentacles and eye-stalks. 
