MUSEUM OF COMPARATIVE ZOOLOGY. 219 



since the discovery of America by European?, and owe its present dis- 

 tribution in the northeast to its being peculiarly adapted to colonization. 

 I have elsewhere related my successful attempt to colonize the allied 

 H. nemoralis* 

 Burlington, N. J., June, 1873. 



* Before closing I will continue the note to p. 202, which suggests some of the 

 changes which would be caused in the pulmonale fauna of Eastern North America 

 by a subsidence in the continent of eight hundred feet. In the Southern Begion 

 the change would be still greater. All the species peculiar to it, catalogued on p. 

 213, would perish, excepting Bulimulus alter natus. This species would still be found 

 in Kentucky, restricted to a small area; all record of its former wide distribution 

 being at the same time destroyed. 



The West Indian and South American species, catalogued on p. 214, would no 

 longer be found on the North American Continent, nor would any record be pre- 

 served of the former connection of the regions. Indeed, no one would then suspect 

 that the tropical genera Gland'ma, Veronicella, and Cylindrella had ever been repre- 

 sented on this continent. 



The West India Islands being much more widely separated from North America, 

 the presence among them of the small American species (catalogued on p. 214) 

 would be still more difficult to explain. 



Again, the supposed subsidence would destroy most of the species peculiar to the 

 Sub-Begion of Texas (see p. 215), and remove the evidence of the present inter- 

 mingling of the North American and Mexican faunas in that Sub-Begion. 



Another effect would be to remove from our reach all evidence of the origin of 

 our species in Bost-pleiocene days, the fossil deposits in the bluffs being rendered in- 

 accessible. Thus one would not be able to have correct impressions of the origin 

 and distribution of certain species. The non-pulmonate Hclicinat give the best in- 

 stance of this. Finding Helicina orbiculata and occulta confined to the narrow limits 

 of the Appalachian Island, one would have no reason to suspect their past history 

 has been so much more interesting than that of many of the species of Stenotrema, 

 etc., found with them, which never had had a larger distribution. It would be im- 

 possible to know that Helicina orbiculata and occulta flourished greatly in Bost-pleio- 

 cene times ; that later, one of them, occulta, became comparatively rare and restricted 

 in range, while orbiculata became very numerous in individuals over a vast extent 

 of territory; and finally, that our supposed subsidence gradually restricted them to 

 the Appalachian Island. 



This supposition of subsidence might be carried still further, till we should have 

 in certain islands of the Appalachian chain the sole resting-places of the now widely- 

 distributed Eastern North American fauna. The more southern of these islands 

 would alone retain the species of the present Cumberland Sub-Begion, and thus be 

 much richer in species than the more northern islands. On the other hand, these 

 more northern islands would possess species derived from the present northern 

 regions which would not be found in the southern islands. 



