TO GEOLOGY. 127 



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 J\felanice, 

 and therefore cannot be placed in the genus Turbo. It 

 'cannot be placed in the genus Rissoa, being umbilicated. 

 In eight species of Rissoa 9 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" 



