4l6 NEW YORK STATE MUSEUM. 



forms by Dewitz and Noetling. American paleontologists have thus 

 far paid no attention to the intracameral structures of the cephalo- 

 pods and it is to be expected that the study of our large Lower 

 Siluric cephalopod faunas will furnish important additional data 

 bearing on this problem. 



Holm does not adopt Dewitz's view that the pseudosepta were 

 " Hilfskammerwande " formed by the animal during a pause in its 

 advance in the shell, but rather concurs with Woodward's older view, 

 that they were a sort of cast-off membranes, though he does not as- 

 sume with the latter author that they originated through con- 

 traction of the layer lining the inner walls of the chambers. He holds 

 that they formed a membranous double bag which was not coales- 

 cent with the mantle and, covering its posterior part, was cast off 

 and left behind when the animal left the old chamber, and later 

 became calcified.^ 



In the European forms the pseudosepta are described as extend- 

 ing from the upper margin of the chambers to the middle of the 

 siphuncular segment. From the structure of the organic deposits 

 in V . o p p 1 e t u m we conclude that here the pseudosepta ex- 

 tended from the upper outer margins of the chambers to their 

 lower inner margin or the neighborhood of the beginning of the 

 septal necks. The structure of the siphuncular wall, which is here 

 that of a Vaginoceras would suggest that the pseudosepta extended 

 through or caused the collarlike interspace which enters between 

 the septum where it bends into the septal neck and the septal neck 

 of the next younger septum which at this point also bends slightly 

 outward \^see pi. 4, fig. 3]. 



The observation of the extremely heavy deposit of organic car- 

 bonate of lime in the chambers and siphuncles of this species natu- 

 rally invites inquiry into its function. Barrande,- I believe, observed 

 the first organic deposit in the chamber of orthoceratites and, 

 pointing out that it appears to be analogous to that in the large and 

 complicated siphuncles of Endoceras, Huronia and Actinoceras, sug- 

 gested that it was secreted by the animal to give strength and weight 

 to the shell. 



^ The peculiar " Pseudoseptalfalten " observed by Holm in the species 

 of Ancistroceras, do not seem to exist in this species of Endoceras, nor 

 have they been found by Holm in the two species of Orthoceras from 

 which he records the presence of pseudosepta. 



2 Syst. Sil. du centre de la Boheme, v. 2, t. 4, p. 280. 



