92 
PLANORBIS radiatus. 
TAB. CXL. — Fig. 5 . 
Spec. Char. Lenticular, radiated; left side um- 
bilicate ; volutions nearly concealed ; aperture 
obcordate. 
This is a strong shell; the radii are a kind of plaits gra= 
dually disappearing towards the margin and very sharp 
but not deep in the umbilicus : the mouth adheres, with 
swelling edges to the next whorl ; about one fourth of its 
diameter in thickness. 
When describing the Planorbis in general, I could not 
help thinking it convenient to describe a shell from the 
micaceous green sand formation, and rather mixed with 
marine with fresh water products, and which may, per- 
haps, hereafter, with further information, lead to the 
separation of another Genus. It is remarkable for forming 
nearly the whole whorl on one side and having small 
indistinct inner whorls. In this green and micaceous 
sand we also find inner casts like fig. 8. 
PLANORBIS euomphalus* 
TAB. CXL. — Fig. 7, 8, and g. 
Spec. Char. Depressed,, subcar mated, concern 
trically striated ; right side flat ; left side 
largely umbilicate ; aperture sub triangular. 
hokls five or six, exposed, gibbose and rather an- 
gular on the left side, forming a deep umbilicus ; the 
aperture receives a slight impression from the preceding 
whorl. The striae are fine all over the shell, and here and 
there, upon the flat side in particular, are a few larger, 
more prominent ones. 
This shell has been described as from the Isle of Wight, 
by Mr. Webster, in the Geological Transactions : my 
spemines are from the mass Mr. Iremonger gave me in 
1808, containing several of the preceding species. I 
believe it differs sufficiently from the French species. 
Fig. 8 and 9 represent casts, apparently of this shell, 
they were sent me by Mr. Davies, of Bath, found in the 
neighbourhood ; occasionally such types may be useful : 
they are Limestone. 
