152 MOLLUSCA. 
central thread. Aperture rounded oval, canal very short, callus scanty 
on the columella, with a boss posteriorly. 
Length three-tenths of an inch; breadth one-eighth of an inch. 
Obtained at Wilson’s Island. Couthouy. 
The characters of this little shell are somewhat negative, but on the 
whole it may be distinguished by its sharp, revolving lines having a 
tendency to granulation, without longitudinal folds ; the little blotches 
in the region of the rostrum seem to be constant. It is a little like C. 
lacteum, Kiener, but much smaller. 
Figure 171, front of the shell, enlarged; 171 a, natural size; 171 8, 
details of sculpture. 
CERITHIUM JANTHINUM (Gould). 
Testa parva, tenuts, ovato-lanceolata, violacescens sed labro, sutura et 
varicibus albis: spira acuminata, anfractibus ad decem trivaricosis 
filis tenuibus ad octo cinctis, quorum mediano majori et granoso ad 
anfractus apicales: apertura ovato-rotundata; rostro brevissimo ; 
columella vix callosa. 
Cerithium janthinum, Gout; Proceed. Boston Soc. Nat. Hist., iii. 
121. May 1849. Expedition Shells, 62. 
SHELL small, rather thin, elongated, ovate-lanceolate, of a pale 
violet colour, with the lip, sutural zone, and varices white; tip acumi- 
nated and of a deeper colour; surface sculptured with fine, raised, 
revolving lines, of which there are about eight or nine on each whorl ; 
spire of about ten whorls, convex, those of the apex rendered angu- 
lated by the central thread being raised and somewhat nodular. 
There are three prominent varices on each whorl. Aperture rounded- 
ovate, canal very short; callus on the columella very sparing. 
Length three-eighths of an inch; breadth three-twentieths of an 
inch. 
