STUDY OF THE GRAPT0LITE8. 



Fie. 15. 



Fig. 13. Fig. 14. 



In another form with similar angular cellules, Graptolithus {Ccenogra'p- 

 tus) gracilis^ figs. 17, 18 and 19,* we have the following illustrations of 

 the mode of occurrence of the species: 



Fig. 17. 



Fig. is. 



We have still another group, presenting some differences, more par- 

 ticularly in the development and form of cellules, than in their general 

 features or mode of growth ; and seeming in some species to unite the 

 characters of those having a single range, with those having a double 



for which the specific name of surcularis will be appropriate, while the entire group will require 

 to be separated under a distinct generic or sub-generic head, for which I propose the name Cceno- 



GRAPTUS. 



* The fig. 19 was theoretically constructed, but has since been verified by the discovery of a 

 specimen having the same form and arrangement of parts. 



