410 NEW YORK STATE MUSEUM 



Observations. This common and characteristic cephalopod of. the 

 Chazy formation of New York is so similar in its form, dimensions, 

 position and character of siphuncle, suture etc. to C. brainerdi 

 from the Upper Beekmantown beds of the same region, that a direct 

 genetic connection between the two species suggests itself very 

 strongly; and there is no doubt that if a continuous series of forms 

 from the Beekmantown to the Upper Chazy types could be obtained, 

 interesting facts in regard to the developmental tendencies. of this 

 race of cephalopods could be ascertained. If the primitive char- 

 acters resting in the presence, relative size and development of the 

 nepionic bulb are taken in consideration as indicators of de- 

 velopment, the Chazy form had not progressed materially beyond 

 the Beekmantown species, the principal progress consisting in the 

 partial incorporation of the nepionic bulb into the phragmocone. 

 The group of large Trenton forms, comprised under the specific 

 name Endoceras proteiforme, which also has the aspect 

 of being a member of the same stock, has proceeded, as far as 

 present evidence goes, to a complete incorporation of the apical por- 

 tion of the siphuncle within the phragmocone, or in other words 

 to the formation of cameras in the nepionic stage. 



Billings [1865, p. 173] has described as Orthoceras velox, 

 a large cephalopod with nearly identical characters — notably in the 

 small depth of the chambers, the rate of growth and size — from the 

 Chazy formation of the Mingan islands, the islands of Montreal and 

 Bizard. The most important difference between the two similar 

 species I find to consist in the different relative width of the si- 

 phuncles which in C. t e n u i s e p t u m is about one half of the 

 width of the phragmocone in mature specimens, in O . velox 

 only one third. Besides, in O . velox the conch is slightly 

 curved, probably a difference of little import. 



Numerous specimens of C . t e n u i s e p t u m , specially those oc- 

 curring near Little A'lonty bay, appear to be much more closely 

 septate than they actually are. This misleading impression is due 

 to the fact that the incrustation proceeding from both the upper 

 and lower walls of the cameras, produces a sharp division line in 

 the middle of the same, which has the appearance of a further 

 septum. The extension of the septal necks to the preceding septum 

 only and the observation of the endosipholining in the apical conch 

 warrants the reference of the form to the genus Cameroceras, as 

 emended bv Hyatt. 



