and Affinities of GraptoKtes. 375 



a woodcut accompanying Mr. Hopkinson's description of the 

 specimen lately published in the present Journal*. Now, after 

 a full consideration of Hall's and Hopkinson's descriptions 

 and a careful examination of Mr. Etheridge's specimen, while 

 I admit the probability of the appendages in question be- 

 longing to the generative system, I am unable to satisfy 

 myself that they are the remains of gonangia. Indeed 

 they do not appear to me to be capsular bodies at all, but 

 rather double laminge, though the way in which they are occa- 

 sionally folded over on themselves, as seen in Mr. Etheridge's 

 specimen, may give them the deceptive appearance of having 

 been capsules, while in reality this condition would be incon- 

 sistent with their alleged capsular form. 



The regularity of their disposition, and the close resemblance 

 between those of the American specimens and those of the 

 British, will not allow us to regard them as mere parasitical 

 or accidental growths ; and I believe that their connexion with 

 the generative system of the graptolite may be considered 

 probable. If so, then it remains for us to determine the parts 

 which represent them in the living hydroid ; and these I believe 

 will be found in the leaflets which compose the corbulse, or 

 basket-shajjed receptacles of the generative capsules, in Aglao- 

 phenia (fig. 5). 



The two rows, then, of appendages in the graptolite would, 

 according to this view, represent a corbula ; and the gonangia 

 or generative capsules, if such had existed, would have been 

 borne upon the front of the graptolite along the bases of the 

 appendages. We should hardly, however, expect to find any 

 remains of gonangia in the fossil ; for in all living hydroids 

 which have their gonangia protected by corbula these go- 

 nangia are as delicate and perishable as the naked generative 

 sacs in the Gymnohlastea. 



The corbula3 of the graptolites, if such really had existed, 

 were probably open ones, like those of the living Aglaoplienia 

 myriophyllum^ and of several species from extra-European 

 seas — a condition which indicates a low stage of differentiation, 

 and represents a form through which the closed corbula of 

 Aglaojjhenia pluma &c. passes in the course of its develop- 

 ment (fig. 5, A, B, C, & d) . 



The view here adopted of the nature of these supposed ge- 

 nerative capsules in the graptolite receives support from the 

 fact that in eveiy case where they have been satisfactorily 

 observed the denticles of the graptolite become suppressed 



* See 'Ann. Nat. Hist.' for IsUw 1871. 



