14 ; GENUS DOLIUM. 
render the aperture of the shell narrower than in the preceding 
species. I think that the Mauea crassilabris of the same au- 
thor, described also in the same work, is only a variety of the 
shell in question. It evidently presents all its characters, ex- 
cepting some slight distinctions of little importance: it is a little 
smaller; the spire is a little more developed, and the right lip 
thicker. 
DIVISION OF THE TUNS INTO TWO GROUPS. 
A. Spectes with the right lip always thin and undulated. 
D. perdix, Lam. The partridge tun. 
— olearium, Lam. — onion-peel tun. 
— galea, Lam. — fluted tun. 
— maculatum, Lam. — speckled tun. 
— variegatum, Lam. —- variegated tun. 
B. Species with the right lip more or less widened by the 
margin, and pretty strongly denticulated. 
D. fasciatum, Lam. The banded tun. 
— pomum, Lam. — helmet-formed tun. 
— latilabre, Nobis. — broad lipped tun. 
