10 



melting of icebergs, by wbich the materials had been trans- 

 ported. The shells are almost invariably broken, but not worn, 

 their angles of fracture remaining sharp. 



Mr. Desor said that it had been thought that the coarse 

 drift near Boston is glacial in its origin. The fact that 

 shells had been found in it had been offered as an objec- 

 tion. This had been explained by the supposition that a 

 glacier had entered the sea at the point. where the shells 

 had been found in the drift. The existence of a layer of 

 clay containing shells beneath the coarse drift at Point 

 Shirley would seem to indicate a quiet deposition, at vari- 

 ance with the glacial theory. 



Mr. Desor read a report on Mr. Wilson's report to the 

 present Congress of the United States, on the swamps and 

 overflowed lands of Louisiana. He gave a minute analysis 

 of its contents, showing it to be of great interest for its 

 scientific statements, and of great value in its bearing upon 

 the domestic interests of the Stat'e of Louisiana. 



Prof. Wyman exhibited the shell and sternum of the 

 Trionyx ferox. He said that the specimens were interest- 

 ing as showing the homologies in the shell of tortoises. 

 Cuvier had first directed attention to the traces of true ribs 

 on the under surface of the shell, and Geoffroy St. Hilaire 

 had found in the under shell a true sternum consisting of 

 the typical number of bones as in many vertebrata. The 

 specimen exhibited showed true vertebree and true ribs on 

 its under surface, and the outer surface was covered with 

 dermal plates resembling the scales of crocodiles, thus unit- 

 ing the endo- and exo-skeletons. A similar union has been 

 pointed out by Mr. Owen in the under shell. The general 

 condition of the shell of the Trionyx fcrox is embryonic in 

 its type, corresponding to the immature state of Emys picta, 

 as Prof. Wyman demonstrated by comparing specimens 

 side by side. 



A specimen of American Swan, (Cygnus Americanus,) a 



