14 PROCEEDINGS OF THE CALIFORNIA 
westward, we also find the few older forms developing into many ‘‘specialized’’ 
varieties. 
Going south of California we find further confirmation of the theory of 
southward migration in Mexico, where species closely resembling the Pomatia 
of Europe occur on the higher mountains, which, unless special creations, 
could only have reached the two regions by a process like that I have described. 
The genera Bulimus, Glandina and Clausilia may also have traversed a similar 
route, though their absence in the tertiary strata of the Eastern States seems 
to be evidence to the contrary. They may, however, be found in the tertiary 
of the Great Basin, which is known to contain fossils of some other genera 
now found only south of the United States (Berendtia and Holospira). Indica- 
tions, however, are known, which point to a connection of tropical regions 
by land in tertiary times, independent of a polar route. The supposed 
‘‘Atlantis ’’ connecting South America with Africa would also have connected 
it eastwardly with Asia and Oceania. 
The humble and despised snails thus become among the most important 
evidences of geological changes and conditions of the land, climate, etc., in 
the past history of the globe. Being terrestrial and easily fossilized when of 
moderate thickness, they furnish evidence not supplied by any other class of 
fossils, while their persistency of types is shown by the close resemblance 
of the carboniferous species to modern tropical forms. One species at least, 
which still lives in the Eastern States, is found only fossil in England (in 
Pliocene or later strata) like the trees found under similar conditions, and 
careful examination of fossil forms on both continents will no doubt show™ 
other curious coincidences. 
It may be mentioned also that genera of abundant occurrence in the Eastern 
States have a few representatives in Europe and Asia, as they have on this 
Coast. 
Hyery fact like this tends to prove that their former migrations have not 
been to the east or west, but from a common northern centre toward the south. 
On Shelis of the West Slope of North America. 
No: LL: 
BY J. G. COOPER, M. D. 
Genus Henrx Linn. A very thorough investigation of the subject with the 
aid of all the light afforded by the works of Pfeiffer, etc., has brought me to 
the conclusion that the Linnean type of Helix must be a form very different 
from Pomatia, and probably including the Californian banded forms. After 
excluding Planorbis, a prior genus, Pythia, and perhaps others, not agreeing 
with the diagnosis, the first Linnean helicoid land-shell is H. lapicida. Al- 
though this does not agree well with the diagnosis in form, it has been shown 
by Morch to be of the same genus, as to the soft parts, lingual teeth, etc., as 
H. arbustorum, aud probably H. Hispana, which are typical in form, and were 
*See Vol. III, pp. 62, 259, 294, 331, IV, 92, 150, 171, V, 121, 172, and Amer. Jour. Conch. 
Zz 
