In the coal measures we also meet, for the first time in our ascending progress, the land snails so familiar now in every part of the world, and which are represented by two little species found in the coal formation of Nova Scotia. The figures of these must speak for themselves; but the fact of their occurrence here and the mode of their preservation require some detailed mention. The great province of the Mollusks we have carried with us since we met with the Lingulæ in the Primordial, but all its members have been aquatic, and probably marine. For the first time, in the Carboniferous period, snails emerge from the waters, and walk upon the ground and breathe air; for, like the modern land snails, these creatures no doubt had air-sacks instead of gills. They come suddenly upon us--two species at once, and these representing two distinct forms of the snail tribe, the elongated and the rounded. They were very numerous. In the beds where they occur, probably thousands of specimens, more or less perfect, could be collected. Were they the first-born of land snails? It would be rash to affirm this, more especially since in all the coal-fields of the world no specimens have been found except at one locality in Nova Scotia;[N] and in all the succeeding beds we meet with no more till we have reached a comparatively modern time. Yet it is very unlikely that these creatures were in the coal period limited to one country, and that, after that period, they dropped out of existence for long ages, and then reappeared. Still it may have been so. [N] Bradley has recently announced the discovery of other species in the coal-field of Illinois. THE TWO OLDEST LAND SNAILS. [Illustration: Fig. 14.--_Pupa Vetusta_, Dawson. (_a_) Natural size, (_b_) Enlarged, (_c_) Apex, enlarged, (_d_) Sculpture, magnified.] [Illustration: Fig. 15.--_Conulus Priscus_, Carpenter. (_a_) Specimen enlarged, (_b_) Sculpture, magnified.]