﻿Cephalopoda of the Cincinnati Group. 



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CEPHALOPODA OF THE CINCINNATI GROUP. 

 By Prof. Joseph F. James, 



Custodian Cincinnati Society of Natural History. 



The class Cephalopoda is represented in the rocks of the Cincinnati 

 Group as exposed in this vicinity by six genera. Thirty-seven species and 

 two varieties have been catalogued as found in the Group. The number 

 given by the present writer is thirty-one species, which seem to be well 

 characterized, two new species being described. The genus Orthoceras is 

 the largest and has thirteen species. Endoccras and Cyrtoccras come next 

 with five and six each. Lituitcs with four, Colpoccras with one and 

 Gomplioccras with two. All but four of the species belong to the straight, 

 longicone shells, the four species of Lituitcs being the only coiled ones. 



The two orders into which the class is divided are best distinguished 

 by the absence or presence of the external shell. All those species of 

 which remains have been found in this locality were provided with an 

 external shell, generally straight, divided into chambers called septa, each 

 of which is connected with its neighbor by means of a tube known as the 

 siphuncle. The animal lived in the outer chamber of the shell and formed 

 a wall across the one behind it, in which it had before resided. The 

 Nautilidic or Nautilus Family is the only one now living of this order, the 

 other two families, Orthoceratidte and Ammonitidce, being known only by 

 fossil representatives. 



Of the three families the OrtJioccratidw is the oldest, having represen- 

 tatives well developed in the lowest fossil bearing rocks. The Ammonitidce 

 is most common in the secondary formations, particularly the Cretaceous, 

 Jurassic and Liassic, while the Naulilidcc ranges from the Lower Silurian 

 age to modern times. Some species of Orthoceras attained a length of 

 six feet, and some Ammonites were three feet in diameter. 



Annnonites did and Nautili do float with the shell down and the tenta-. 

 cles expanded on the surface of the water, but creep on the bottom 

 with the shell raised on the back. Orthoceras, on the other hand, is sup- 

 posed by Woodward to have swum in a perpendicular position, head 

 downwards. Whether they crept on the bottom with a six-foot tower on 

 their backs can not now be determined. 



It has long seemed to the writer a remarkable fact, that, in spite of 

 the amount of palaeontological work done by innumerable writers, so few 

 attempts have been made to collect the scattered descriptions and render 



