37 



haps the most constant of all genera to the tj-pical form. 

 It iB to be remarked that all these syphonated shells are 

 carniverous. The Strombus and other large molluses are, 

 in the Tropics, the scavengers of the sea shore. Those 

 ■with entire mouths, on the contrary, are generally vegetable 

 feeders. Thus ■whenever you meet with a shell with a 

 canal or a notched mouth, you may be sure it is a Marine 

 Shell and belongs to a carnivorous family. There are 15 

 families of Marine Holostomata or entire mouthed 

 Univalves, but as this discourse is of shells in general and 

 none in particular, it would simply be tedious to enumerate 

 them. Except some species of Turbo, and certain Tropical 

 Limpets, which spread out to the size of a cheese- 

 plate, none of them are large shells. All the 

 land molluscs are of the order Pulmonifera, or air breathers, 

 and their shells entire-mouthed : there are four families of 

 land shells, the most important and extensive of which 

 are the Helicidae, the typical genus being the Helix or snail, 

 comprising about 1,200 species, world-wide in their distri- 

 bution. According to the best authority, Turtcn's British 

 shells, edited by Dr. Gray, there are 72 species of this 

 family in Great Britain, 28 of which belong to the Genug 

 Helix, or J snail proper. Many of the shells belonging to 

 the Genus Pupa, Clausilia, Cylindrella, and Balea, a 

 group of small pointed shells, less known than the snails, 

 from being generally smaller, more retired in their habits, 

 and more local .in their distribution. Nor are the several 

 species of shells to be found everywhere, their local 

 distribution being influenced by soil and vegetation, and 

 gome are scarce. The Helix Aspersa, the common 

 brown snail, is universal. The Helix Hortcnsis is also very 

 generally spread. There are several varieties of this species , 

 among which is the beautiful black and yellow banded 

 snail, as powerful in its colouring, if not so lively, as many 

 tropical shells. The largest British species is the Helix 

 I'limatia, or Roman snail, so called because it is said to have 

 been introduced by the Romans as an article of food, it is, 



