322 NEW YORK STATE MUSEUM 



Growth stages of Cameroceras brainerdi WhMeld 



STAGE 



Embryonic stage 



Nepionic 

 stage 



or larval 



SUBSTAGES 



Neanic or adolescent 

 stage 



Ephebic or mature 

 stage 



Ananepionic 



Metanepionic 



Paranepioiiic 



CONDITION OF CONCH 



Protoconch not retained 



Ananeanic 



Metaneanic 



Paraneanic 



Anephebic 



Metephebic 



Parephebic 



The conch is at first but an open- 

 unchambered, conchiolinous 

 shell (ananepionic substage). 

 With further growth a part, 

 of the space inclosed within 

 the conch is set apart by septa 

 as cameras, and thus the 

 phragmocone or chambered 

 portion of the conch becomes 

 separated from the open cone 

 (metanepionic substage). Then 

 the nepionic bulb becomes 

 filled by endosiphosheaths and 

 intercalated organic carbonate 

 of lime (paranepionic sub- 

 stage). 



Continued growth of the animal 

 necessitates continuous forma- 

 tion of cameras and of endosi- 

 phosheaths and leads to a widen- 

 ing of the siphuncle and the sepa- 

 ration of an endosiphotube and 

 endosiphocoleon. 



The siphuncle is open, separated 

 from the phragmocone by the 

 ectosiphuncle (contiguous septal 

 necks) in the anterior portion; 

 by the ectosiphuncle and endosi- 

 pholining in the posterior por- 

 tion. The endosiphocone is 

 bounded hy the final endosi- 

 phosheath. Further growth 

 of the conch is only apparent 

 along the apertural margin of 

 the living chamber. 



6 Relations of Proterocameroceras to Cameroceras, Vaginoceras and 



Nanno 



A reference of our species to any of the genera of the Endo- 

 ceratidae is beset with considerable difficulty. A short historic 

 review of the varying generic references of the two most nearly 

 related forms, Vaginoceras belemnitiforme and 

 Nanno aulema, will demonstrate this. The first form with 

 a free apical cone or nepionic bulb was described by Holm as 

 Endoceras belemnitiforme [1887, p. 5]. The author 

 of the species named stated that it is unknown whether the 



