134 ' CONCHOLOGY. 



T. oheliscus. The obelisk Trochus. 



Species not umbilicated, conic, elevated, flat and circular 

 base ; the termination of the columella strongly twisted, 

 but passing down by the margin, appearing sloped by the 

 advance of an internal longitudinal plait. 



T. iris. The iris Trochus. 



Species not umbilicated, conic, base oblique ; aperture 

 large, slightly angular ; the columella twisted, and forming a 

 kind of tooth at its termination. 



T. granulatus. The granulated Trochus. 



Conic, imperforate at the base, spirally granulated and 

 not marginated at the edges of the volutions ; body swelling 

 out ; spire tapering abruptly ; apex acute, flesh-coloured. 



T. umbilicaris. The umbilicated Trochus. 



Shell conico-convex, rather flat, rounded at the top ; apex 

 depressed, volutions sub-marginate ; striated spirally ; aper- 

 ture compressed and angular ; umbilicus large, extending to 

 the apex ; colour whitish. 



3, Monodonta. Twenty-three species. 



This genus occupies an intermediate space between the 

 Trochus and the Turbo ; distinguished from the former by 

 the aperture being more round and slightly depressed, and 

 from the latter by the toothlike projecting angle which the 

 truncated columella occasions at the base of the aperture. 



Shell ovate or conoid, aperture round and entire, with an 

 operculum ; outer lip disunited from the body at the top ; 

 columella arched and truncated at the base. 



Monodonta bicolor. Monodonta tectum. 



M. pagodus. M. labio. 



M. tectum Persicum. M. AustraUs. 



M. papillosa. M. canalifera. 



M. coronaria. M. viridis. 



M. Egyptiaca. M. fragarioides. 



M. carchedonius. M. constricta. 



