CONCHOLOGY. 135 



M. modulus. M. tricarinata. 



M. articulala. M. canaliculata. 



M. lugubris. M. Seminigra. 



M. punctulata. M. rosea. 



M. lineata. 



M. coronaria. The crowned Monodonta. 



Species in which the columella greatly projects, and the 

 spire is entirely flat ; covered with numerous small tuber- 

 cles ; colour white ; the columella tinged with red. 



M. lahio. The double-lipped Monodonta. PL 23, fig. 2. 

 Species sub-globular, umbilicated, spiral whorls rounded ; 

 the columella terminated by a tooth. 



M . fragarioides . The strawberry-shaped Monodonta. 



Species more or less globular, of which the columella, al- 

 most straight, offers but a little obstacle to its junction with 

 the margin. 



4. Turbo. The Turban Shell. Thirty-four species. 



Distinguished from the Monodonta by never having the 

 columella truncated at the base ; and from the Trochus by 

 being solid, with the whorls constantly convex and never flat- 

 tened. Like the Trochus, when decorticated, the Turbo ex- 

 hibits splendid pearly, gold, or silver irridescent colours. 



Shell thick, pearly in the interior ; depressed, conical, or 

 sub-turreted ; umbiHcated or not, little or not carinated at its 

 circumference ; aperture round or little depressed ; the mid- 

 dle of the external edge not bent, but sometimes hollowed or 

 sloped in some part ; the edges rarely joined by a callosity ; 

 the columella arched, rarely twisted, and not truncated at the 

 base ; operculum calcareous or horny ; the spire visible ex- 

 ternally in the latter and interiorly in the former ; the exte- 

 rior often thickened and curved. 



Turbo marmoratus. Turbo diaphanus. 



T. imperialis. T. rugosus. 



T. torquatus. T. coronatus. 



