167 



equal valves; and it is move common in gasteropods than in 

 acephala. 



Dr. Gould expressed the belief that the geographical distribu- 

 tion of unios would throw much light on generic distinctions, and 

 that each large basin would be found to possess its peculiar ani- 

 mals. 



Prof. Agassiz observed that this relation was especially observ- 

 able in regard to fishes, though they have peculiar facihties for 

 changing their locality. He instanced the Rhine, Rhone, and 

 Danube, which in their head waters in Switzerland contained the 

 same fishes ; while lower down, the fishes of each river are not 

 only different from each other, but those of the lower portion are 

 difi^erent from those in the upper. 



A specimen of the Odontaspis griseus^ described by Mr. 

 Ayres as Carcharias griseus, was presented by Dr. D. H. 

 Storer. 



This is a rare shark on our coast ; the specimen, a female, was 

 about four feet long. On each side of the teeth at the base was a 

 small toothlet, and the upper lobe of the tail was much longer 

 than the lower, and indented on the lower edge near the tip, dif- 

 fering in this respect from Oxyrhina, (Ag.) in which the upper 

 lobe is but little longer than the lower. 



Prof. Wyman gave an account of some observations 

 on the shedding of the antlers of the American red deer. 



After the rutting season is past, and, in consequence of the 

 stoppage of the circulatiou through them, they have become dry 

 and dead, the antlers are separated from the living frontal bone 

 by a process of absorption carried on by the Haversian canals. 

 These acting on one plane through the whole thickness of the 

 bone just below the " burr," remove the solid materials around 

 them, so that each canal becomes dilated on that plane until its 

 cavity unites with that of an adjoining one. When this process 

 has extended entirely across the base, the antler drops. The fall 

 of the antler was shown to have a close resemblance to the pro- 

 cess by which, in necrosis, the dead is separated from the living 

 bone. 



