THE NAUTILUS. 33 



ture of the water of Cayuga Lake, which even in midsummer 

 is very cold except in sun-warmed shallows. 



It is interesting to compare the present molluscan fauna of 

 Cayuga Valley with its Pleistocene ancestry of which fossil re- 

 mains ' occur in a delta terrace between Toughannock Falls and 

 Frontenac Beach, about twenty feet above the present lake level. 

 These Pleistocene forms include: 



Lampsilis luteola Say. 



Lampsilis ventricosa Barnes. 



Anodonta fragilis Lam., (marginata Say). 



Anodonta yrandis Say. 



Anodonta grandis var. footiana Lea. 



Sphserium simile Say. 



Pisidium compression Prime. 



Pisidium virginicum Bourg. 



Limnaea palustris Mull. 



Limneea elodes Say. 



Physa heterostropha Say. 



Planorbis bicarinatus Say. 



Planorbis deflectus Say. 



Planorbis lentus Say. 



Planorbis parvus Say. 



Amnicola limosa Say. 



Valvata tricarinata Say. 



Campeloma decisa Say. 



These mollusca were approximately synchronous with the 

 Pleistocene forms of the Don Valley beds of the Toronto forma- 

 tion, one-hundred and seventy miles northwest of Ithaca. 

 They apparently lived during the Peorian, or Fourth Inter- 

 glacial Period. The colony was established by Mississippian and 

 St. Lawrence molluscs coming in from the West. After the 

 annihilation of the colony by the advance of the ice, everyone 

 of the interglacial species re-established itself when the ice 

 finally retreated, and all are now living in the waters of Cayuga. 



1 See C. J. Maury, Interglacial Fauna in Cayuga Valley. Journ. of Ge- 

 ology, 1908, vol. xvi, no. 6, pp. 565-5(57. 



