1883.] 253 [Hyatt. 



effect of any unusually severe winter of the present time on the 

 cattle and other animals of our plains, and the circumstances in 

 which the latest fossil remains of horses are discovered ; the man- 

 ner of preservation and petrifaction of the latter being similar to 

 that obtaining in the so-called bone licks of much more recent 

 date. 



Letters were read from Professors Alphonse Milne-Edwards 

 and Josej)h Prestwich and the Marquis de Saporta acknowledging 

 their election as Corresponding Members; and also from Prof. 

 Henri Milne-Edwards acknowledging election to Honorary Mem- 

 bership. 



General Meeting, April 4, 1883. 



The President, Mr. S. H. Scudder, in the chair. Thirty 

 persons i>resent. 



The following paper was read : 



GENERA OF FOSSIL CEPHALOPODA 



BY PROF. A. HYATT. 



Univalve shells may be generally spoken of as cones, which may 

 be either straight, curved, or coiled; and the coiled may be 

 either loosely coiled, or close coiled; either in the same plane, or 

 a descending spiral. The shell-covered Cephalopoda are straight, 

 ex. Orthoceras ; arcuate, ex. Cyrtoceras ; loose coiled, ex. Gyro- 

 ceras ; close coiled, ex. Nautilus. 



The larger number of the more ancient shell-covered Cephalo- 

 poda are straight cones. These predominate in the Silurian over 

 the arcuate, which are often merely varieties of species of 

 the straight cones, as demonstrated by Barrande, and as may be 

 observed in all good collections. The voun<r of nautilian shells 

 are identical with the adults of the arcuate and gyroceran, and in 

 different series repeat their forms, sutures, shell markings and 



1 This paper is preliminary to a monograph which will appear in the Memoirs of the 

 Museum of Comparative Zoology. 



