so 



TERRESTRIAL AIR-BREATHING MOLLUSKS. 



Mesodou exoleta. 



thyroides. 



clausa. 



profunda. 

 Pupa armifera. 



contracta. 

 Succinea obliqua. 

 Helicina 1 orbiculata. 



occulta. 



Polygyra auriformia. 

 Stenotrema stenotremum. 

 hirsutum. 

 mono don. 

 Triodopsis palliata. 

 obstricta. 

 appressa. 

 inflecta. 

 Mesodon albolabris. 

 elevata. 



Of the above all are now living and are equally numerous, excepting 

 Helicina occulta, a species most abundant in Post-pleiocene days, but 

 now almost extinct. 2 The other species of Helicina is now confined to 

 more southern limits. 



In addition to the above, the following species, now living in the Inte- 

 rior Province, probably had their origin in Post-pleiocene times and will, 

 no doubt, be found fossil in the "bluffs" : — 



Zonites friabilis. 



leevigatus. 

 suppressus. 

 indentatus. 

 interims. 

 minusculus. 

 limatulus. 

 Polygyra Dorfeuilliana. 



leporina. 

 Mesodon multilineata. 



Pennsylvania. 



Mitchelliana. 



dentifera. 



Tebennophorus Caroliniensis, Pall if era dorsalis, and Limax campestris 

 probably have also come down from Post-pleiocene times. From their 

 nature they could leave no record of their presence in the " bluffs." 



There are also found in the Interior Region several forms of Succinea 

 of doubtful specific value, which have been described as 



Mesodon bucculenta. 



Sayii. 

 Triodopsis tridentata. 



fallax. 

 Pupa pentodon. 

 fallax. 

 rupicola. 

 corticaria. 

 Vertigo milium. 



ovata. 

 Succinea avara 

 ovalis. 



Succinea aurea. 



Mooresiana. 



Succinea retusa. 



Grosvenori. 

 lineata. 



The following is a complete list of those species of the Interior Pvegion 



1 Though not Pulmonata, these two species are strictly terrestrial in their habits, and 

 are here introduced from their value on the question of the permanence of the Post-pleio- 

 cene species. One of them is almost extinct, the other more restricted in its range at 

 present. 



2 See Vol. I. 183, 184 ; Bland and Binney, Ann. Lye. N. II. of N. Y., IX. 289. 



