A MANUAL OF AMERICAN LAND SHELLS. 35 



America. The subregion is equally prolific Id individuals, and the in- 

 di\idual8 are highly developed. These facts are partially explained by 

 the nature of the country. Low mountains, thickly shaded, well watered, 

 and with a genial climate and proper soil, offer in their thickets and 

 ravines innumerable safe breeding-grounds for the land shells.* Tliere 

 seem also to be in this subregion conditions peculiarly conducive to 

 testaceous variation. Eight of its peculiar species are carinated, and 

 here also the following species of the Interior Eegion show the same 

 tendency to carination : Zonites ligerus, intertextus, Fatula alternata, 

 Triodopsis appressa and palliata. Here, also, we first notice the varia- 

 tion of Patula alternata towards heavy ribs upon its shell, which is 

 still more apparent as the species extends towards the southwest, t 

 Here, also, Mesodvn elevatus is often found banded. M. dentiferus and 

 Sayii are greatly developed. 



The Cumberland Subregion is peculiar for the development of Zonifes, 

 and in the disintegrated genus Helix for the development of the section 

 or genus Stenotrenia, almost peculiar to these narrow limits. 



(c) The Southern Eegion 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 Xorth Caro- 

 lina, South Carolina, Georgia, all of Florida, the southern part of Ala- 

 bama, Mississippi, Louisiana, extending into Texas. | Its boundaries, 

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

 fined. Manv of the species from the Interior Eegion and Cumberland 

 Subregion have spread into its northern portion, and the following have 

 extended over the larger portion of it: 



Macrocyclis concava. Helicodiscus lineatus. 



Zonites fuliginosus. StroMla lahyriiithica. 



inornatus. Stenotrema hirsutum. 



suvpressus. monodon. 



■ indentaius. Triodopsis palliata. 



arboreiis. tridentata. 



minusctilns. • fallax. 



Limax campestris. Van Nostrandi. 



Patula alternata. Mesodon albolahris. 



* See Terr. Moll. U. S., Vol. I, pp. 122, 123. Beiug less adapted for cultivation than 

 the balance of Eastern North America, we may hope for the preservation of onr land 

 shells in this region, while they decrease rapidly before the advance of civilizatiou 

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



tThis heavily ribbed form was common in Post-pleiocene days. 



t See Terr, Moll. U, S., Vol. 1, 120. for a description of the region. 



