404 J. W. Dawson—Paleozoie Land Snails. 
I propose to state some additional facts respecting the species 
already known, to discuss their affinities, and to describe two 
additional species, making six in all from the Paleozoic rocks, 
including one from the Hrian or Devonian. For reasons to be 
mentioned in the sequel, I do not admit the genus Paleorbis 
founded, by some German naturalists, on fossils which I believe 
to be tubes of Annelids. 
t may be useful to premise that of the two leading sub- 
divisions of the group of Pulmonifera, the Operculate and 
Inoperculate, the first has been traced no farther back than the 
Kocen e second, or Inoperculate division, includes some 
genera that are aquatic and some that are terrestrial. Of the 
aquatic genera no representatives are known in formations 
Carboniferous and the early Tertiary, though in the inter- 
vening formations there are many fresh-water and estuarine 
There is perhaps no reason to doubt the continuance of the 
Helicide through this long portion of geological time, though 
it is probable that during the interval the family did not 
increase much in the number of its species, more especially as 
it seems certain that it has its culmination in the modern 
to Bradley, in an underclay or fossil soil which may have been 
the bed of a pond or estuary, and subsequently became a forest 
sub-soil. The Erian species occurs in shales charged with 
remains of land plants, and which must consequently have 
