58 [Assembly 



the branches turn in opposite directions is tlie centre or point of origin of 

 the animal body. It should moreover be observed that the serratures on 

 the two sets of branches are usually turned in opposite directions, or to- 

 wards the two extremities of the rachis. 



Fig. 10. Gkaptolithus gracilis. 



This one and the preceding species are remarkably slender, and, though 

 serrated on one side only, present some marked peculiarities when compared 

 with the singly serrated forms with central discs, and a bilateral arrange- 

 ment of the branches, as in G. logani, G.Jlexilis and G. multifasciatus. 



Among the undescribed fossils from the shales of the Hudson-river group, 

 I have lately noticed a species of Rastrites, a graptolitic genus proposed 

 by Barrande, and which, so far as I am aware, has not before been 

 observed in this country. The similarity of the latter form with the last 

 noticed species of Graptolithus {G. gracilis), suggests a probable re- 

 lationship which may unite the two, or authorise the separation of G. 

 gracilis, G. divergens, and some others, as a generic type distinct from 

 those with central discs and uniserrate stipes. 



