GENUS XXVIII. TVRBO. 125 



of the small tapering species, have certainly not a round mouth, 

 and would seem to belong rather to the Helices than to the 

 Turbines. 



The placing in this genus of shells that vary so much in 

 the form of the mouth, has rendered it extremely difficult to di- 

 stinguish a Turbo from a Trochus on the one hand, or from a 

 Helix on the other. Some alteration here seems highly neces- 

 sary. 



Most of these shells are thick and strong, like the Trochus, 

 and often pearly within ; their shapes are very various : few 

 of the animals have been described ; but that inhabiting Turbo 

 elegans is particularly mentioned by Montagu (p. 34 -t of 

 Testacea Britannicci), being very remarkable : it is the only 

 land species that is known to have a testaceous operculimi : 

 it is also remarkable in having only two horns, with eyes at 

 their base ; the glossy tips of the horns are supposed also to be 

 eyes by Montagvi ; and if that is correct, it will make it still 

 more singular : they are not hermaphrodite, like the rest of 

 the land species, but are of distinct sexes, like most of the 

 water ones : the animals of T. Caryckium and Vertigo are like- 

 wise both land species, with only two horns : it is probable, 

 that there is nmch variety among the animal inhabitants of 

 this genus ; many of them have opercula, some thin and horny, 

 others thick and testaceous. 



Linnaeus makes five divisions: first, Neritoidei; second, 

 Solidi imperforati ; third, Solidi perforati ; fourth, Cancellati ; 

 and fifth, Turriti. 



