PULMONATA. 105 
these authors appear to agree so closely that they must be referred to the same 
species. I have not, it is true, had an opportunity of comparing the English with 
the French shells; the identification, therefore, rests entirely on the figures and 
descriptions given by MM. Brogniart and Deshayes; but, forming my opinion from 
them, I cannot see any sufficient reason for considering the English shells as distinct. 
The present species is a small lenticular shell, slightly concave on each disc, but more 
so on the upper than on the under side: the whorls are four or five, each embracing 
nearly one half of the preceding whorl; they are slightly convex on both surfaces, but 
more so above than beneath, and acutely angulated round the periphery, a little below 
the middle of the whorl. The aperture is of an elongated heart-shape, and not very 
oblique. 
Brogniart describes his shell as swelled out (bombé) and lenticular rather than 
umbilicated; and this, owing to the slight concavity of the discs, may be taken as 
the general character of the English shell. M. Deshayes, whose figures are drawn 
from the original specimen, states that in Brogniart’s figure the shell is represented 
with the sides too much swelled out, and with the marginal angle too near the 
middle. Making due allowance for these errors, it will be seen that the contour of 
the shell and the form of the aperture represented by Brogniart’s middle figure, agree 
very well with those of the English specimens.* In the figure given by Mr. Sowerby 
the aperture is represented as very obcordate, and it conveys the idea of the whorls 
and the shell being more convex than they really are. M. Bronn, in his ‘ Lethea 
geognostica,’ (p. 1011,) states that the shell described by Mr. Sowerby is more 
depressed than that of the typical P. dens, and he refers it to a distinct species, which 
he has named P. Sowerbyi. I fear that M. Bronn had not authentic specimens of our 
P. lens before him ; for the figures he has given (Tab. XL, fig. 17 a—c,) do not correctly 
represent that shell; but they, as well as his description, agree closely with another of 
our Eocene Planorbes, which I have therefore referred to his species. The P. /ens of 
‘Mineral Conchology’ appears to me, as I have already stated, to correspond so closely 
with Brogniart’s P. /ens, that the two cannot be separated. 
Férussac quotes Brard’s Planorbe anguleux as a synonym; but whether the present 
species really is the same cannot well be determined without reference to the 
original specimen, as both the description and the figure given by Brard are too 
imperfect for the purpose of identification. I have, however, followed the example of 
MM. Brogniart and Deshayes, in quoting Brard with a query. 
Size—Diameter, 3-10ths of an inch nearly. 
Localities—Hordwell, and Headon Hill, where it is moderately plentiful. rench: 
Saint-Chaumont, Pantin, Limagne, Cournon. 
* Judging from the aperture, Brogniart’s figures are reversed, probably owing to an oversight of the 
artist. 
“14 
