MOLLUSCA; 109 
eyes at the tips of the two longest. This contains the fol- 
lowing British species, viz. bidens, perversa, biplicata, plica- 
tula, and labiata. The other genus, called Verrrico, was 
formed by Miiller. The animal possesses only two tenta- 
cula, with the eyes on their tips. The T. vertigo is the 
type of the genus. 
28. Hextix. Linneus, in constructing this genus, at- 
tended only to the character of the mouth being contract- 
ed or lunated, without regarding the habits of the animals, 
or even the other forms which the shells exhibited. Hence 
he has united globose, discoid, and turreted, terrestrial, flu- 
viatile, and aquatic shells ; animals with two and with four 
tentacula, with and without an operculum, oviparous and 
viviparous. } 
The marine species of Linnzeus are few in number. The 
genus JANTHINA of Lamark, has been formed from the H. 
janthina of Linn. a species of which has lately occurred at 
several places of the Irish coast. The opening is triangu- 
lar, and there is an angular sinus at the right edge. The 
shell, which Linnzeus terms H. haliotoidea, is completely 
concealed in the animal. There are many marine shells 
inserted in the genus Helix by British writers, which either 
belong to the restricted genus Turbo, or to the Vermicu- 
laria. 
The further reduction of the Linnzan helices depends 
on the separation of the terrestrial from the fluviatile shells, 
and subdividing these according to the characters furnish- 
ed by the different groups. 
Among the terrestrial shells, the restricted genus HELIX 
is by far the most extensive. It contains those shells which. 
are subglobose, with a convex spire; the opening entire, 
wider than long, and diminished in its upper part by the 
