4 I2 



NEW YORK STATE MUSEUM 



C . tenuiseptum, specially in the frequent septation and the 

 thinness of the septa. On the other hand its siphuncle does not 

 attain the large relative width of that of the latter species. Also 

 from ( O . ) v e 1 o x Billings, to which it bears considerable 

 similarity in its curvature, closeness of septa and marginal position 

 of the relatively large siphuncle, it can be distinguished by the still 

 closer arrangement of the septa and the smaller size of the 

 siphuncle. 



It appears that in this form as in C . t e n u i s e p t u m the fre- 

 quency of the septa is correlated to their extreme thinness ; and that 

 the organic deposits of the cameras served in part the purpose of 

 counteracting a lack of strength in the septa. 



Genus vaginoceras Hyatt 



The genus Vaginoceras Hyatt, with V . multitubulatu m 

 Hall (sp.) as type was originally defined by Hyatt [1884, p. 266] 

 as follows : 



The funnels extend posteriorly beyond the next septum to that 

 from which they originated. The sheaths are very numerous, and 

 continuous, according to Whitfield, with the funnels. Endosiphon 

 unknown. 



The diagrammatic section of Endoceras by the same author in 

 Zittel-Eastman's textbook as well as the reference of Endoceras 

 b e 1 e m n i t i f o r m e of Holm to Vaginoceras, indicates that Hyatt 

 did no longer support Whitfield's view as to the direct connec- 

 tion of the septal necks and endosiphosheaths. This point 

 can, however, be cleared fully only by an investigation of the 

 genotype, V. m u 1 1 i t u b 11 1 a t u m , a form of which it is difficult 

 to obtain specimens suitable for this work. We have here referred a 

 single form to Vaginoceras and this reference requires explanation. 



The enlarged section of the ectosiphuncle of this form, reproduced 

 in plate 4, figure 3, shows that each septal neck extends to the second 

 preceding septum where it rests on the septal neck, the place being 

 marked by a white spot that contrasts with the black carbonaceous 

 substance of the ectosiphuncle. There appears to have remained 

 just above the end of the septal neck, a vacant ring which later 

 on has been filled with infiltrated white calcite. 



A like vacant ring has been indicated by Hyatt in a diagrammatic 

 section through the siphuncle of Endoceras p r o t e i f o r m e , 

 given in Zittel-Eastman's textbook. The presence of this vacant 

 space and the observation of a collarlike extension of the lumen of 



