BEEKMANTOWN AND CHAZY FORMATIONS OF CHAMPLAIN BASIN 493 



ventral lobes, large moniliform siphonal beads, perforated with 

 radiating canals. 



The principal features of the structure of Gonioceras are the ex- 

 treme depression of the shell and the extended lateral flanges. Hyatt, 

 in his first publication on the classification of the cephalopods [1884] 

 thought this genus extraordinary enough to erect a separate family 

 for its reception, adding that its features warrant his "assuming this 

 as probably one of the passage forms from the compressed Ortho- 

 ceratites. above described, to the true Sepioidea, and possibly a more 

 or less remote ally of Paleoteuthis dunensis Roem. of the 

 Devonian." In regard to this view it has been stated by Foord 

 [1888, p. 323] that the shell of Gonioceras was certainly external, 

 while that of the sepioids is internal. Hyatt himself has later on 

 advanced to another hypothesis on the derivation of the sepioids 

 and placed Gonioceras [1900, p. 528] at the end of the Actinocera- 

 tidae, evidently considering it as an aberrant group, related to 

 Actinoceras, with which genus it is connected by the structure of its 

 siphuncle. 



This genus is not only odd in its structure but equally peculiar 

 in its distribution. It is restricted to the American basin, where it 

 has thus far been observed to have spread in the Trenton period 

 from New York to Wisconsin. In New York it has, however, only 

 been found in one locality, viz, at Watertown, where the genotype 

 occurs not infrequently in the Black river beds. In Europe it is 

 entirely absent and it belongs therefore to the most characteristic 

 forms of the American basin of the Lower Siluric era. In the rocks 

 deposited in this basin it again has thus far been found 

 to be restricted to those of Trenton age, and it has not been found 

 in the Trenton rocks of the Appalachian basin. In view of this 

 remarkably restricted geologic and geographic distribution of the 

 two species of Gonioceras, the finding of a third species in the pre- 

 ceding Chazy beds and in an exposure lying within the Appalachian 

 basin is of special interest, not only indicating a possible center of 

 origin for the genus, but also in regard to the relation of the Chazy 

 Appalachian basin to the Trenton American basin. We shall have 

 occasion to recur to this relation in the chapter on the distribution 

 of the Cephalopoda. 



