GRAPTOLITES OF NEW YORK, PART 2 69 



genera are simply gradually dying out, only a few of the most vigorous 

 holding their ground and finally producing the new genera characteristic of 

 the Siluric. Thus the Utica shale only produces the peculiar and rare 

 Dendroid genera Mastigograptus and Chaunograptus, the single Axono- 

 lipous genus Pleurograptus that is monotypic and very short-lived and 

 no new Axonophora at all. The succeeding Champlainic zones have not 

 furnished any new genera and hardly any new species. 



The Devonic has with the exception of a distinctly paracmic species of 

 Monograptus afforded but Dendroidea and in Ptiograptus still produced a 

 most striking new generic type of that order. Thus the Dendroidea are 

 not only the first appearing graptolites but also the last to leave the field, 

 one form of Dictyonema even persisting in America into Carboniferous 

 time. 



ADDITIONAL NOTES ON MORPHOLOGY 

 a Notes on morphology of spines 



In a study of the later graptolite faunas of the Champlainic one can not 

 fail to notice a great increase of spinose forms in comparison to the earlier 

 faunas. The contrast becomes still more marked when the fauna of the 

 third Deepkill zone, where the biserrate forms appear first and which in its 

 general aspect is more similar to the Upper than to the Lower Champlainic 

 faunas, is counted with the former. The spines are in their morphology, 

 the place and time of their appearance and the amount of their development 

 of manifold interest, mainly in regard to the phylogeny of the larger groups, 

 since several authors, most clearly Beecher, have shown that they are in all 

 living beings most sensitive indicators of the degree of development attained 

 by the species. A separate discussion of the numerous spinose forms 

 described in this paper promises, for this reason, to yield a few facts of 

 interest. Besides, such procedure will prevent repetition in the systematic 

 part of the paper. 



We shall see that the spines of graptolites arise from different causes, 

 at different stages of the development of the genera, at different places and 

 are of different morphologic character. At the same time they furnish 



