144 Association of American Geologists and Naturalists. 



so much decayed that it is impossible to recover an entire speci- 

 men ; but one skull was secured whole. 



None of the skeletons are of extraordinai-y size, although the 

 bones in some cases seem more massive than usual. Specimens of 

 the carvings, &c., wei'e exhibited, which, as Mr Squier observed, 

 displayed no inconsiderable skill and taste. 



Professor Agassiz made a communication on the structure and de- 

 velopment of Polypi. He was of the opinion that there was a more 

 intimate relation than had been supposed among the radiated ani- 

 mals. He endeavoured to shew the bilateral character of the Po- 



Mr Dana, of the United States Exploring Expedition, mentioned 

 one or two facts in corroboration of the views of Professor Agassiz. 



Thursdm/^s Proceedings. 



Dr J. C. Warren made a communication upon the subject of the 

 Mastodon. He at first gave an historical account of the discovery of 

 the different skeletons now existing. He shewed that the Mastodon 

 and Elephant belonged to the same family of Pachydermata or thick- 

 skinned animals. The proper name is Mastodon giganteus. In the 

 skeleton of this animal the great preponderance of the anterior 

 parts is to be observed, the head, tusks, and vertebrae of the neck. 

 Tlie posterior portions of the animal are greatly inferior in size to 

 the anterior. The head of the Mastodon is greatly flattened on its 

 upper surface, differing in this respect widely from the head of the 

 Elephant, the facial angle is smaller than in the Elephant, the cavity 

 of the cranium is smaller. The difl'erence between the teeth of the 

 Elephant and Mastodon were explained, and the growth of the teeth 

 commented upon. It was shewn that the teeth did not all grow at 

 one time, but at different pei-iods. He also pointed out other pecu- 

 liarities and distinctions. The perfect state in which the bones are 

 found, he attributed to their exclusion from atmospheric air. Their 

 antiquity he could not pretend to detail, but it must be very great. 



Professor Agassiz made a remark or two in relation to the sub- 

 ject. 



Dr Warren said that some persons had attempted to make out 

 thirty species of Mastodons. He had been enabled to make out 

 only three — the Angustideus, the Humboldteus, and the Giganteus. 



Mr Dana read a paper upon the laws or cohesive attraction, as 

 exemplified in crystallization. The following are the inferences 

 which he drew : — 



1. Cohesive attraction is charactei'ised by fixed angles, as regards 

 the direction of its action, and by specific relations of force in cer- 

 tain axial directions, and it differs in those particulars for different 

 substances. 



