* 
~ 
TO GEOLOGY. 12 
GENUS TUBA.  (nobis.) 
Description. Shell conical, umbilicate; whorls round- 
ed; mouth round; margin not united above ; columella 
thickened and reflected at the base. 
This genus is nearly allied to Turbo and to the Rissoa 
of Freminville ; but not being able, with propriety, to 
place it with either, I propose to constitute for it a new 
genus. The reflected margin, which is disposed to be 
effuse, has at the base some similarity to the Melanie, 
and therefore cannot be placed in the genus Turbo. It 
cannot be placed in the genus Rissoa, being umbilicated. 
In eight species of Rissoa, in my cabinet, all are thickened 
round the margin, forming a varix. ©The Tuba has no 
thickening of this kind, the margin being crenulate. The 
Rissoa has an acute apex, while that of the Tuba is 
almost truncate, the superior whorls being smooth and 
gibbous. Mr Sowerby’s Mineral Conchology, plate 395, 
figures a shell (Turbo sculptus), which, I think, should 
be placed in this genus. It is from the London Clay of 
Barton. Of it, and the preceding one, he says, they “do 
not agree precisely with the character of the genus Turbo 
of Lamarck,” and further, “they form a passage towards 
Delphinula.” . 
