1874.1 235 [Ingersoll. 



Oxynoticeras Guibalii Hyatt. 



Amm. Guibalii Reynes' Plates (pars). 



Amm. Guibalianus Reynes' Plates (pars). 



The keel of this species may begin to disappear even at the size 

 of 100 mm. In one specimen in the Semur collection this is accom- 

 panied by a singular and marked lateral deflection of the hollow keel, 

 and at the size of 170 or 180 mm. it has wholly disappeared. The 

 outer whorl then has a very broad, gibbous abdomen, the sides remain- 

 ing convergent and rounded. 



Oxynoticeras Lotharingum Hyatt. 



Amm. Lotharingus Reynes' Plates. 



In this species at the size of 100 mm. the keel has almost disap- 

 peared and the ribs in several instances cross the abdomen. The 

 abdomen becomes rounded but the involution did not appear to de- 

 crease perceptibly in the specimens examined. The umbilicus is 

 smaller in the adult, the whorls stouter in proportion and the charac- 

 teristic form and aspect of O. Guibalianus is found only in the young. 

 The extreme young stages have no hollow keel; it is a characteristic 

 of the later periods of growth and of the adult, and then disappears 

 in the oldest stage. This is perhaps the most interesting instance I 

 have yet discovered of the polarity of the senile and young stages of 

 the life of the individual. The resemblances which exist between 

 them in other characteristics are intensified by the disappearance in 

 old age of this important structure. 



Prof. R. H. Richards exhibited some photographs of large 

 masses of copper, found at Isle Royal, Lake Michigan, which 

 bear hammer marks made by the prehistoric inhabitants of 

 that region. 



The thanks of the Society were voted to Prof. H. A. Par- 

 ker and Mr. D. B. Fay for donations to the Museum. 



December 16, 1874. 

 The President in the chair. Forty-five persons present. 



Mr. Ernest Ingersoll, of the United States Geological 

 Survey, gave an interesting account of the domestic life of 



