8 



Prof. Agassiz concluded that there is no general law regulat- 

 ing the distribution of the Chelonians of North America. They 

 are distributed through four grand divisions of the country, a 

 northeastern, a southern, a western, and a Pacific range. The 

 facts of their geographical distribution are now well established, 

 but the reasons are by no means evident at present. The proba- 

 bility is, that different individuals of the same species of animals 

 are adapted, by peculiar organizations, to different climacteric 

 influences, and that there is no general law of distribution for 

 which physical agents can account. 



Dr. Storer asked what was the northern geographical limit of 

 Cistudo Blandingii. In 1842, he presented to the Society a 

 specimen from Bradford, Mass., until which time it had not 

 been observed by naturalists north of South Carolina. 



Prof. Agassiz replied that he had found the eggs in Massachu- 

 setts, and raised the animal from them. There is no evidence of 

 its existence between Massachusetts and Illinois, where it is 

 again found. It has a circle of distribution in the Northwestern 

 States, and another disconnected range in Massachusetts. He 

 thinks the animal may have originated in the two different 

 localities. 



The President exhibited some Fossil Bones and Teeth, 

 discovered by Mr. J. W. Foster, in Iowa. They consisted 

 of remains of an animal belonging to the natural family 

 of SuidaB, and appeared closely allied to, if not identical 

 with the Euchserus of Dr. Leidy. A complete series of 

 teeth was exhibited, in which the milk and permanent 

 molars were all represented. A large portion of the 

 skeleton, as well as the germs of the teeth of a very 

 young animal, belonging to the same species, were ex- 

 hibited, indicating that they were derived from an indi- 

 vidual which had been born but a short time, or even 

 from a foetus. 



Dr. Durkee exhibited a potato infested with a parasitic 

 insect, a species of Acarus. A new generation is pro- 

 duced every few weeks. The gentleman who gave him 



