GRAPTOLITES OF NEW YORK, PARI 2 Iig 



Axonophora from the Axonolipa the proper inference is that in the latter 

 the siculae were produced in the same locality, i. e. at the base of the nema- 

 caulus or on the primary disk; but with the difference that in the Axonolipa 

 they all were discharged and in the Axonophora only a part, the remainder 

 stow in £ out to additional rhabdosomes. 



Another astogenetic character, at least of the genera Diplograptus and 

 Climacograptus, that bears on the phylogeny of the Axonophora is the 

 initial downward growth of the first theca of the rhabdosome along the 

 sicula [see text fig. 6] ; for this can not be otherwise explained than as a 

 relic of the time when all thecae of the rhabdosome grew forward or away 

 from the center of the rhabdosome, as they did in the majority of the 

 Axonolipa. 



The origin and position of the virgula within the nemacaulus has been 

 briefly noted by the writer in Memoir 7 [p.551] and the evidence of its gen- 

 eral existence in the Axonophora more fully given in this paper \antca p. 96]. 

 As the hist step to its formation we ma)' probably consider the thickening 

 of the dorsal wall of the common canal in certain Dichograptidae, as 

 Tetragraptus amii [see Mem. 7, p. 552], for it is probable from this 

 that the solid rod has become separated in the course of further develop- 

 ment. Its first appearance in the sicula in the astogeny of the Axonophora 

 we have there considered as a case of tachygenetic transference of a char- 

 acter acquired in later development to the embryonic or postembryonic 

 stage (the sicula). 



The statement made in Memoir 7 with special reference to the 

 Dicranograptidae, that the virgula of the Axonophora may not be an 

 homologous organ in all genera, has lost its meaning by the recognition 

 that the Dicranograptidae do not have any virgula and are properly 

 considered as Graptoloidea Axonolipa [see p. 102]. 



Both Diplograptus and Climacograptus appear side by side in the third 

 Deepkill zone before any of the Dicranograptidae have come on the scene, 

 and their chronological order hence invalidates possible attempts to connect 

 the Climacograptidae — and eventually also the Diplograptidae — with the 



