122 NEW YORK STATE MUSEUM 



other than the remaining' species ; C . antiquus being the probable 

 ancestor of C. cauclatus; C. modestus forms together with C. 

 scharenbergi a natural group; and C . b i c o r n i s represents another 

 group. 



We have before set forth that, in our opinion, the development of 

 apertural spines has induced the formation of a system of supporting 

 ledges, lateral axes, and fibers within the periderm and has thus, combined 

 with the influence of the obvious tendency of the holoplanktonic graptolites 

 to lighten their periderm without accruing loss of strength [sec Mem. 7, 

 p. 5 18 J, led finally to structures as we find them in the genera Retiograptus 

 and Retiolites. It is here shown under the heading Glossographts that 

 forms which have hitherto been considered as typical Diplograpti, as 

 notably D. quadrimucronatus, may already under the thick outer 

 periderm possess the structure above referred to. We have, for this 

 reason, referred these forms to Glossograptus. But it is evident that such 

 a form which in all its external features is still a typical Diplograptus, is 

 transitional from Diplograptus to Glossograptus. Since highly spinose 

 types of Glossograptus appear already in the third Deepkill zone, together 

 with the other early Axonophora, it is probable that the Glossograpti devel- 

 oped from different stocks at different times and that the genus is poly- 

 phyletic. How rapid the development has been at the dawn of the order 

 Axonophora is clearly evinced by the fact that also Retiograptus appears 

 already side by side with Diplograptus and Glossograptus. 



Retiograptus eucharis has been here, on account of its spinos- 

 ity, referred with some doubt to Glossograptus. It certainly is not con- 

 generic with the genotype of Retiograptus (R . t e n t a c u 1 a t u s) and has 

 the thecae of a Diplograptus. We are probably not far from the truth in 

 considering it, on account of its thecal form, as a descendant of Diplo- 

 graptus i n u t i 1 i s , a species of the third Deepkill zone, for both possess 

 not only similar small dimensions but also the same concave outer margins 

 of the thecae and slightly recurving denticles ; and D. inutilis already 

 exhibits a distinct tendency to the formation of spines at the thecal aper- 



