74f SHELLS AND SHELL-FISH. PART I. 



or at least without spines^ or very prominent nodules. 

 The typical genus is Terebra, — the longest spired group 

 of all the carnivorous gastropods^, but so closely resem- 

 bling TurrUella, that the difference in their apertures 

 alone distinguishes the shells. In the genus Bucciiium, 

 the spire is much shorter^ and the body-whorl more 

 ventricose. These seem to be the typical groups. The 

 three aberrant will be now described. The first, which 

 appears to us to make the nearest approximation to the 

 wide-mouthed genus Microtoma, is Leiodomus, founded 

 upon two shells, the animals of which have been beauti- 

 fully figured* by M. Quoy. One of these is the Bucci- 

 num Icevigatum of authors; the other, XheB.Achatinum.f 

 Both these have the foot of an immense size, so that it 

 spreads over a circumference near three times as large 

 as the shell, and is sufficient to envelope it entirely. In 

 other respects there are some slight points of variation 

 between the two; but they do not strike us, at present, 

 of sufficient moment to sanction the formation of sepa- 

 rate genera. To these we add the Terebra vittata j, 

 and three or four other species, apparently undescribed. 

 The vittata, however, appears aberrant, and leads im- 

 mediately to Terehra. We are disposed to consider, 

 also, as the type of another genus ( Trochia), the species 

 of Purpura of that name, — since its characters will 

 not agree with those of Purpura, while the striated 

 inner lip leads to the conjecture that it is a prototype or 

 Oniscia and similar shells. Lastly, we have, in Tri- 

 tonidea §, a remarkably varied group of small shells, 

 some of which resemble Triton, and others Buccinum; 

 the base, however, is always contracted, and even slightly 

 produced ; the pillar marked at the base with elevated 

 granulations, or short obsolete plaits ; and a distinct canal 

 at the top of the aperture. The connection of this group 

 to Buccinum is very obvious, while its union to Triton 



* Encv. Mcth. j)l. 400. fig. 1. 



f Ibid. pi. 400. tig. 4. J Ibid. pi. 402. fi?. 4. 



^ I have since learned that this genus is the same as Po/li'n Gray. — a 

 name 1 should gladly liave adopted, had it not previously been given to a 

 genus of European Lcpidoptcra. 



