212 BULLETIN OF THE 



There seems also to be in this Sub-Region conditions peculiarly condu- 

 cive to testaceous variation. Six (or twenty-five per cent) of its pe- 

 culiar species are carinated, and here also the following species of the 

 Interior Region show the same tendency to carination, — Zonites Ugerus, 

 intertextus, Patula alternata, Helix appressa and palliata. Here, also, 

 we first notice the variation of Patula alternata towards heavy ribs upon 

 its shell ; which is still more apparent as the species extends towards 

 the southwest.* 



The Cumberland Sub-Region is peculiar for the development of 

 Zonites, and in the genus Helix for the development of the section or 

 subgenus Stenotrema, almost peculiar to these narrow limits. 



(c.) The Southern Region comprises the peninsula of Florida, with 

 the adjacent islands, together with the alluvial regions of the Atlantic 

 and Gulf coasts. It includes, therefore, the eastern portion of North 

 Carolina, South Carolina, Georgia, all of Florida, the southern part of 

 Alabama, Mississippi, Louisiana, extending into Texas.f Its boundaries, 

 however, are but imperfectly known, and probably not accurately de- 

 fined. Many of the species from the Interior Region and Cumberland 

 Sub-Region have spread into its northern portion, and the following 

 have extended over the larger portion of it : — - 



Macrocyclis concava. Helix fallax. 

 Zonites fuliginosus. albolabris. 



inornatus. thyroides. 



suppressus. Pupa pentodon. 

 indentatus. fallax. 



arboreus. armifera. 



minusculus. contracta. 



Limax campestris. rupicola. 



Patula alternata. corticaria. 



Helix lineata. Vertigo milium, 

 labyrinthica. ovata. 



hirsuta. Succinea avara. 

 monodon. obliqua. 



palliata. Tebennophorus Caroliniensis. 



tridentata. Pallifera dorsalis. 



of our land shells in this Region, while they decrease rapidly before the advance of 

 •civilization elsewhere. See Ibid., pp. 132, 133. 



* This heavily ribbed form was common in Post-pleiocene days. 



t Sec A. Binney, Terr. Moll. U. S., I. 120, for a description of the Region. 



