PAPERS OX GEOLOGY AND GEOGRAPHY 413 



paimlate as in the recent form. Specimens of each form 

 are measured below, the recent form being from Canan- 

 daigua Lake, N. Y. 



"^Tiorls 5, height 6.3; max. diam. 15.7; min. diam. 11.3 mm. Recent. 



Whorls 5, height 6.0; max. diam. 12.6; min. diam. 10.0 mm. Recent. 



Whorts 5. height 5.1; max. diam. 12.6; min. diam. 10.3 mm. Marl. 



"Whorls 5, height 4.6; max. diam. 11.5; min. diam. 8.5 mm. Marl. 



Planorhis deflecfus Say. Xot common. The form 

 with the acutely keeled periphery. 



Platiorhis arcticus Moller. About a dozen specimens 

 of a small Planorbis occur in the marl material that are 

 indistinguishable from specimens of arcticus from the 

 Great Slave Lake region. Thev were at first identified 

 as hirsutus but are quite different from undoubted hirsu- 

 tus from Massachusetts. It is not surprising that this 

 Arctic species should be found in Pleistocene deposits, 

 because the natural migration of these mollusks must 

 have been by way of the Mississippi Valley and their 

 remains would naturally be left in some of the ancient 

 waterways. A single specimen of the same form was 

 found in marl deposits near Eush Lake, Logan Co., Ohio, 

 collected by Dr. M. M. Leighton. It was listed as hirsu- 

 tus in Journ. Geol., Vol. XX^^II, p. 449. 



Planorhis altissimus (Baker). Abundant and variable. 

 This, the common small Planorbis of Pleistocene de- 

 posits, appears to be related to arcticus and is, perhaps, 

 the ancestor of that species. As the latter is rare in 

 Pelistocene deposits and common in the recent fauna 

 in high latitudes this hypothesis seems reasonable. 

 Xumerous specimens of a small Planorbis from Devil's 

 Lake and other places in Xorth Dakota, collected by Miss 

 Mina L. "Winslow, of the Museum of Zoology, LTniversity 

 of Michigan, are to be referred to arcticus and not to 

 altissimus, as stated in a paper recently published 

 (Journ. Geo., Vol. XXX, p. 54, 1922.) Altissimus is not 

 surely known from the recent fauna. 



Planorbis parvus urbanensis Baker. This, one of 

 the smallest of the Planorbes, discovered in Pleistocene 

 deposits near L'rbana, was found to be fairly common in 

 the Joliet fauna. As it has also been found in Carroll 



