BEEKMANTOWX AND CHAZY FORMATIONS OF CHAM PLAIN BASIN 405 



chamber, the extension of the septal necks to the preceding septum 

 and the presence of the endosipholining. 



YYe adopt here these genera since we have had occasion to observe 

 the varying lengths of the septal necks and the presence of the 

 endosipholining in some forms and its apparent absence in others. 

 As to the endosiphosheaths we infer from our material that they 

 are present in all these genera in like close arrangement and fre- 

 quency, but not in equal preservation, becoming in some more calci- 

 fied than in others. Indeed the diagram given by Hyatt in Zittel 

 Eastman's textbook shows them in great number in Endoceras. 

 while that genus had been defined as possessing but few. The 

 statement in regard to Cameroceras is due to the formation of a 

 thick final endosiphosheath by the senile cephalopod. Drawings, 

 distinctly showing this thick sheath as well as the endosipholining 

 of Cameroceras,. have been given by the writer. 1 



The assertion made by Whitfield [1881, p. 25, fig. 2] in regard to 

 the genotype, V. m u 1 1 i t u b u 1 a t u m, that the endosiphosheaths 

 are continuous with the septal necks in Yaginoceras, needs veri- 

 fication, for the endosiphosheaths have certainly no connection 

 with the septal necks in the other two genera nor could any such 

 connection be inferred from Holm's careful sections of Endoc- 

 eras b e 1 e m n i t i f o r m e [1895, pi. 22, fig. 9] , 2 which species 

 is referred to Yaginoceras by Hyatt. The septal necks, which in 

 that species reach beyond the preceding septum, are represented as 

 gradually thinning out upon the older septal necks. This condi- 

 tion corresponds to that found in the other genera. 



The siphuncular structures of the endoceratid forms of the 

 Trenton which are the types of these genera need further investi- 

 gation before the relations of the latter can be considered as being- 

 cleared up. 



Cameroceras (Proterocameroceras) brainerdi Whitfield (spj 



Plate 1, figure 5, 6 ; plate 2, figure 1 



Orthoceras brainerdi Whitfield. Am. Mus. Xat. Hist. Bui. lSvS. 



v. 1, no. 8, p. 319, pi. 27. fig. 14-16 

 Orthoceras e x p 1 o r a t o r ( Billings) Whitfield. Am. Mus. Xat 1 1 st 



Bui. 1890. v. 3, no. 1, p. 33. pl- 2, fig- 3 



'An. Rep. State Paleontol. for 1903. X. V. State Mus. Bui. 80. 1905. pi. 9. 

 fig. 2. 



2 Copy in An. Kep't State Paleontol. for 1903. X. V. State Mas. KuV 80. 

 3905. text li",. 19. 



