77 
Plate VI. Fig. 1, is the upper side, and Fig. 3, the under side, of a 
limestone fossil, not very uncommon, I believe, in the neighbourhood 
of Bath. It is somewhat of a discoidal, or rather of a plano-concave 
form, and is in general from two to three inches in breadth. Its spiral 
convolutions, which are from four to five in number, are strongly 
carinated, in the direction of the turns, on nearly the middle of the upper 
side, and become slightly grooved towards the next inner turn. On 
the under side, they are of a roundish form, and marked with slight 
but frequent oblique rugae ; the turns being so disposed as to form, in 
the under part, a tolerably smooth funnel -formed cavity. In one species, 
distinct nodular projections exist on the lower side of the spiral turns. 
None of the specimens which I possess are in sufficiently good 
preservation to allow me to speak decidedly respecting the aperture 
of this fossil. I am only enabled to observe, that none of the preceding 
whirls project into the hollow of the next ; as, from my specimens 
being fractured in several places, I am able to perceive that the ridge 
on the upper part of the shell is a solid external projection, which no 
ways affects the circular cavity of the shell. Hence there is reason 
to conclude, that the mouth is round, and not diminished by the pro- 
jection into it of the preceding whirl, as takes place in the planorhites. 
This fossil was first described by Mr. Walcot in these words : 
“ Depressed, volutions three, a sharp ridge runs in the centre of the 
upper surface of the volutions. Lime- stone.” Descriptions and 
Figures of Petrifactions, 8fc. Fig. l. and lvi. 
As far as I am able to judge, from such parts as have not suffered 
injury, or are not concealed by the adhering matrix, the fossil 
represented Plate VI. Fig. 7 and 8, is another species of the same 
genus, in which the preceding fossil should be placed. It is discoidal ; 
but the central projecting termination of the spire is elevated in a 
peculiar manner, so as at first sight to give it the appearance of being 
detached from the next turn. On closer examination this is, however, 
found not to be the case ; since a connection is formed by an 
