GEOGRAPHICAL DISTRIBUTION. 35 



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

 have extended over the larger portion of it : 



Macrocyclis concava. Triodopsis Van Nostrandi. 



Zonites fuliginosus. Mesodon albolabris. 



inornatus. thyroides. 



suppressus. Pupa pentodon. 



indentatus. fallax. 



arboreus. armifera. 



minusculua. contracta. 



Limax campestris. rupicola. 



Patula alternata. corticaria. 



Helicodiscus lineatus. Vertigo milium. 

 Strobila labyrinthica. ovata. 



Stenotrema hirsutum. Succinea avara. 



monodon. obilqua. 



Triodopsis palliata. Tebennophorus Caroliniensis. 



tridentata. Pallifera dorsalia. 

 fallax. 



Equally wide over the Region has been the distribution of those 

 minute species whose origin has been traced to circumpolar regions (see 

 p. 26). Such are: Zonites viridulus, fulvus, and Vallonia pulchella. 



In addition to these species derived from the north, are found the fol- 

 lowing species peculiar to the Region, whose origin can be traced to the 

 south, in the peninsula of Florida, from whence, indeed, many of them 

 have not yet spread over the whole Region : 



Glandina truncata. Mesodon major. 

 Zonites cerinoideus. jejuna. 



Polygyra auriculata. Mobiliana. 



uvulifera. Bulimulus Floridanus. 



Postelliana. Dormani. 



espiloca. dealbatua. 



avara. Cylindrella jejuna. 



cereolus. Pupa variolosa. 



septemvolva. modica. 



Carpenteriaiia. Succinea effusa. 



Febigeri. campestria. 



pustula. Wilsoni. 



pustuloides. Veronicella Floridana. 

 Triodopsis Hopetonensis. 



Of the more widely spread species, Polygyra septemvolva is repi'esented 

 by various forms over the whole southern littoral region, both of the 

 Atlantic and Gulf. So is Glandina truncata, Mesodon jejuna, Polygyra 



