A Manual of Elementary Geology / or, The Ancient Changes of the Earth and its Inhabitants as Illustrated by Geological Monuments

by Sir Charles Lyell

Fig. 42.

Neritina globulus. Paris basin.

Fig. 43.

Nerita granulosa. Paris basin.

Some naturalists include Neritina ([fig. 42.]) and the marine Nerita ([fig. 43.]) in the same genus, it being scarcely possible to distinguish the two by good generic characters. But, as a general rule, the fluviatile species are smaller, smoother, and more globular than the marine; and they have never, like the Neritæ, the inner margin of the outer lip toothed or crenulated. (See [fig. 43.])