GRAPTOLITES OF NEW YORK, PART 1 543 



This disk is not present in young individuals and continues later on to grow 

 in correspondence to the size of the whole colony. Its formation presupposes 

 an enveloping tissue. 



4 There appear secondary spines and other appendages, mostly at the 

 distal end, as in Climacograptus bicornis, which, lying outside of 

 the thecae, attain a greater size and development than the individuals 

 supposed to have lived in the small thecae, could have given them by their 

 action. 



5 There is found in some forms, as in Lasiograptus, an external frame- 

 work consisting of horny filaments, which would suggest that it served to 

 protect this soft covering tissue. 



Finally we mention, that it has been claimed bj- Giimbel that the periderm 

 consisted originally of chitin, though tests recorded by Wiman showed that 

 no reaction, characteristic of chitin, is any longer obtainable from the fossils ; 

 that it can not be doubted that it once consisted of some chitiulike substance ; 

 and, further, that the periderm possessed a certain degree of elastic flexibility, 

 for the nemas and rhabdosomes are frequently found bent and twisted with- 

 out having been broken. 



10 Classification and phylogeny of the graptolites 



a Review of classifications. As the systematic arrangement of the 

 organisms is to express their true relationship, it is evident that no arrange- 

 ment can find general acceptance so long as the investigations on the morpho- 

 logic and phylogenetic relations of a group of forms have not passed beyond 

 their inceptive stages. This fact impresses itself at once on the paleontologist 

 who attempts to find a generally adopted system for the classification of a 

 graptolite fauna under investigation ; for he will soon observe that not only 

 the larger divisions which suggested themselves so readily, but also many of 

 the genera which once appeared so well defined and compact, have lately lost 

 and are still losing in value as natural groups. 



It was natural that a grouping of the graptolites began with a separa- 

 tion from the graptolites proper of the arborescent forms grouping them- 



