504 NEW YORK STATE MUSEUM 



similarly breviconic and rapidly expanding; nor do any of the 

 Trenton species of the State invite comparison with the possible ex- 

 ception of the genotype of Oncoceras, O. constrictum, 

 which, however, is readily distinguished by the much greater con- 

 striction of its living chamber. O. exignum Billings (sp.), a 

 Canadian Black river form, is much more slender and less curved. 

 Not any of the species of Oncoceras from the western Trenton, made 

 known partly by Hall and partly by Clarke, bear any similarity with 

 O . p r i s t i n u m . 



This is a true Oncoceras in the short, small form of the shell, 

 as well as in the position and character of the siphuncle. The 

 living chamber however is distinctly contracted in apertural direc- 

 tion, but the aperture appears to have remained open. 



While in its congeners the apical part of the phragmocone as a 

 rule is missing and probably has been cast off by the animal, in this 

 form the phragmocone is, with the exception of the last two cameras, 

 filled solidly with calcite — sometimes to the degree of obscuring all 

 structure — and in such a fashion that a solidifying of this part of 

 the shell by organic deposition of carbonate of lime suggests itself. 



The habitat of this small peculiar form seems to have been the 

 sponge fields for it is found most frequently associated with species 

 of the common Chazy sponges of the genus Strephochetus, which 

 almost alone compose certain layers of the Chazy formation and 

 which also have constantly overgrown the shells of this cephalopod. 

 Among these sponge masses the diminutive cephalopod would seem 

 to have found favorable conditions of shelter and preying. 



FORMAE INCERTAE SEDIS 



Orthoceras (?) primigenium (Vanuxem) ? Whitfield 



Orthoceras primigenia Vanuxem. Geol. N. Y. 3d Dist., 1842. 



p. 36, fig. 4 

 Orthoceras primigenium Hall. Pal. N. Y. 1847. 1:13, pi. 3, 



fig. II, iia 

 Orthoceras primigenium Whitfield. Am. Mus. Nat. Hist. Bui. 



1889. V. II, no. 2, p. 56, pi. 10, fig. I 

 Orthoceras primigenium Cleland. Am. Pal. Bui. 1900. no. 13, 



p. 20 



Vanuxem figured a small orthoceratite among the fossils of the 

 Calciferous group, and stated in a short note that its chambers are 

 numerous and near to each other, that the terminal parts are solid 

 and that it is found in considerable number in the quarry opposite 

 Fort Plain in the Mohawk valley. Hall in his first volume of the 

 Palaeontology of New York figured a group of similar apical parts 

 of the conch and also a fragment of a more anteriorlv situated 



