116 GASTEROPODA. LIMNADZ. 
Helix nautilea, Mont. Test. Brit. 464. pl. 25. fig. 5, fig. mala. 
Turbo nautileus, M. & R. Trans. Linn. Soc. viii. 169; Turt. 
Conch. Dict. 227; Dill. Desc. Cat. 882. 
Planorbis cristatus, Drap. Hist. Nat. des Moll. 44. pl. 2. figs. 
2, 0. 
Planorbis nautileus, Flem. Edinb. Encyel. vii. 69. 
Animal cinereum aut griseum. Tentacula hyalina. Oculi atri. 
Habitat in paludibus, stagnis. 
’ Shell with its left side rather flat ; the epidermis of the whorls 
transversely elevated; the keel obsolete and tuberculated. 
Diameter one-eighth of an inch. 
Animal ash-coloured or grey. Tentacula hyaline. Eyes 
black. 
Planorbis imbricatus was first noticed by Miiller. The epi- 
dermis is subject to very great variation, with regard to the de- 
gree in which it is elevated. The specific character is taken 
from the most common appearance. In some situations it may 
be found with a smooth epidermis, with every intermediate 
state, necessary to prove its identity with the one above de- 
scribed. The dorsal ridge is sometimes furnished with spine- 
like processes of epidermis. 
It seems to be rather a local species. It is found in Batter- 
sea fields ; in a pond, near Tenby ; in ditches, near Sandwich ; 
near Wedhampton, in Wiltshire; round Kingsbridge and Exe- 
ter, in Devon; and ina pond near Cobham, in Surrey. I found 
it in a marsh, near Dunloch Gap ; and again at Muccross, near 
Killarney. 
The preceding pages have been reprinted from a copy in Mr. 
Baldwin’s possession, the work having proceeded so far in 1820 
under Dr. Leach’s revision. The manuscript, contaming the 
remaining species of Planorbis, and the six succeeding genera, 
which was probably at the printers when the work was stopped, 
cannot now be recovered. 
