16 TROCHUS. 



partly closed by a callus deppsit ; columellar lip ending anteriorly 

 in an obtuse dilated callus. Type, E. guamense, Q. et G. 



Genus ISANDA H. and A. Adams, 1854. 



Shell orbicular-colloidal, polished ; aperture longer than wide, 

 subquadrate; umbilicus open, perspective, the margin crenulated. 

 Type, I. coronata A. Ad. 



Genus CAMITIA Gray, 1847. 



Shell orbicular, depressed, smooth, polished; axis imperforate; 

 columella spirally twisted above, forming a false-umbilicus, with 

 the margin simple ; columella with the edge edentulate and ending 

 in a point.. Type, C. pulcherrima Gray. 



China, Japan. 



Genus UMBONELLA A. Adams, 1863. 



Shell globose-conoid, solid, porcellanous, polished, narrowly um- 

 bilicate ; aperture subquadrate, lip simple, dilated anteriorly ; um- 

 bilicus narrow, margin eremite rugose. Type, U. murrea Reeve. 



Japan. 



Genus CHRYSOSTOMA Swainson, 1840. 



Shell globose, solid, thick, spire very short ; aperture rounded, the 

 parietal wall bearing a heavy callus which wholly or almost covers 

 the narrow umbilicus. Type, C. paradoxum Born. 



Genus TROCHUS Linn., 1758. 



Trochus LINN., Syst. Nat., x, p. 756. Pyramidea SWAINSON, 

 Malacology, p. 350. Rochia GRAY, Guide Syst. dtst. Moll. Brit. 

 Mus., p. 148. (1857.) 



Animal with 1 to 4 pairs of cirrhi upon the epipodial line, which 

 are not ciliated ; frontal lobes between the tentacles simple or folia- 

 ted, distinct or united into a vail. The formula of teeth is QC 5 . 1 

 . 5 . oo or co . l-f-5 . 1 . 5-fl . oo. 



The central and lateral teeth have more or less expanded lateral 

 margins, and bear cusps which are smooth on the cutting edge, with 

 minute denticles one or several in number at the sides. There is 

 frequently a narrow oblong plate, without cusp, lying between the 

 5th lateral and the inner marginal tooth, usually more or less con- 

 cealed by the expanded outer margin or supporting-wing of the 5th 

 lateral. This seems to me to be a rudimentary or rather, degenerate 

 lateral tooth ; not the inner marginal tooth, as Dr. Troschel and 



