J8 NEW YORK STATE MUSEUM 



If we compare the size and frequency of the individuals of a number of 

 graptolites in which spinosity is more or less developed, as D i p 1 o g r a p t u s 

 foliaceus, Glossograptus q u a d r i macron at us, Tetragrap- 

 tus fruticosus and Climacograptus bicornis with that of 

 their congeners, we can not avoid the inference that the)' are the most 

 stately and in three of the four also the commonest and most widely dis- 

 tributed species which certainly must mark the acinic development and the 

 period of highest vitality of their races. In C 1 i m acogra t u s bicor- 

 n i s this is combined with such a great variety of modifications, all occurring 

 in the same horizon, that I have here described them separately and inferred 

 that they indicate the period of "zooic maximum" of this stock [see under b]. 



In the genera Glossograptus, Dicranograptus and Dicellograptus, 

 spinose forms appear directly at the outset, in the latter two associated with 

 nonspinose forms. Here the short life of the genera or their very small 

 vertical range has to be taken into account and inferred that their rapid 

 development was followed by so rapid a decline that ascending and descend- 

 ing forms could be separated only by most refined stratigraphic work. I 

 have no doubt, however, that the latter would show an increase of spinose 

 forms in the upper subzones of the Trenton beds. 



The distribution of spines on the rhabdosomes of the graptolites is 

 lastly of interest on account of its bearing on our conception of the grapto- 

 lite colony and of the sicula. The writer has in former papers contended 

 that there are features in the graptolite colonies — such as beginning 

 division of labor, developing symmetry of arrangement, presence of com- 

 mon organs — which indicate that the colonies had begun to progress to 

 a concentration of functions, leading to an approach of the colony to a 

 functional individual, if not to a morphological one. The distribution and 

 development of spines furnishes some further interesting clues along this 

 line of investigation not noted in the former publications. These are the 

 facts that in certain forms as in Glossograptus q u a d r i m u c r o n a t u s, 

 Dip log rapt us foliaceus and C 1 i m a c o g r a p t u s bicornis 

 either the first two thecae may be provided with spines different in position 



