326 



NEW YORK STATE MUSEUM 



The close similarity in the. structure of the apical portion of 

 the conchs of Proterovaginoceras belemniti- 

 forme and Nanno aulema has been recognized by 

 Clarke, Holm and Hyatt. We have found a like nepionic 

 siphuncle in Proterocameroceras brainerdi.. 

 Proterovaginoceras belemnitiforme and Pro- 

 terocameroceras brainerdi have further in common 

 the strong development of the peculiar organ which we have 

 termed the endosiphocoleon, leaving as structural differences, 

 only the different length of the septal necks or funnels and the- 

 presence of the endosipholining in the latter. The phylogenetic 

 relationship or common origin of the Proterovaginoceras-Vagi- 

 noceras series, the Proterocameroceras-Cameroceras and the Nanno 

 series is therefore not to be doubted. Of these again the Vaginoceras 

 series has retained the most primitive characters, as is apparent by 

 the longer septal necks. A Vaginoceras-like form is therefore with 

 great probability to be considered as the common radicle of the entire 

 group. This form, which in the appended diagram we have- 

 designated as '' Protovaginoceras," would have to be looked for in. 

 stages still preceding the late Beekmantown. 



Our view of the relation of the species of Vaginoceras, Cam- 

 eroceras, Nanno and Piloceras^ attained here is expressed in 

 briefer form in the following table. 





VAGINOCEKAS 



CAMEROCERAS- 

 ENDOCERAS 



NANNO SERIES 



PILOCERAS 





SERIES 



SERIES 







Typical or mature 



Vaginoceras 





? (Nanno) 





development 



multitubu- 

 latum 





fistula 

 ? (Nanno) 







(Vaginoceras 



Cameroceras 



pygmaea 



Piloceras 





wahlen- 



trentonense, 









bergi) 



Cameroceras 









(Vaginoceras 



protei- 









vaginatum) 



forme 









etc. 









Proteroforms 



Proterovag- 



Proterocam- 



Nanno au- 



(Protero- 





inoceras 



eroceras 



lema 



piloceras) 





belemniti- 



brainerdi 









forme 









Protoform 



Protovagino- 

 ceras 









^See chapter 8, p. 329. 



