GUAPTOLITES OF NEW YORK. PART 1 483 



practicable, while the presence of distinctive features makes the creation of 

 certain new terms imperative. 



As numerous terms have been applied to almost every part of the 

 graptolite structure, it is advisable to define the terms here used before 

 entering on a description of the forms and a discussion of their structure. 



The term hydrosome means "the whole colony" in the terminology of 

 the hydrozoans. For the whole colony of the graptolites the terms frond, 

 polypary, polypidom, polypier, polypariet, colonie and Stock also have been 

 used. Tornquist has proposed to use for hydrosome the more neutral term 

 rhahdosome, which has been adopted by Wiman. The rhabdosome of a 

 graptolite could be defined as each colony which- originates from a sicula. 

 Here arises, however, a difficulty from the fact — discussed fully in the 

 chapters on embryology and morphology of the graptolites — that, while in 

 the Dendroidea and Dichograptidae each colony originates from one sicula, in 

 the later forms, the Axonophora (Diplograptus etc.) generations of secondary 

 colonies, produced by the primary colony, and each of which also originates 

 from a sicula, remain in connection with the mother colony and thus form a 

 compound colony or a person of a still higher order (the bushlike stocks 

 of Diplograptus etc.). These are hence colonies of colonies, or a combination 

 of rhabdosomes. It would probably be advantageous to apply to these com- 

 bination colonies a term like synrhahdosome, expressive of their composite 

 character.^ As formerly the "stipes" (rhabdosomes) of Diplograptus, 

 Climacograptus and other later genera were considered as representing the 

 whole colony, the terms hydrosome, rhabdosome, polypariet etc. have been 

 applied to these as well as to the entire colonies of the Dichograptidae and 

 Dendroidea. This usage happens to be correct in consequence of the homology 

 of both now recognized. 



* The writer has in a previous paper on Diploi^raptus [1895, p. 22 1] termed the 

 compound colonies of Diplograptus hydrosomes and the component colonies rhabdosomes, 

 a usage which, however, does not appear to express the homology existing between the 

 components of the Diplograptus colony and the whole colony of the Dichograptidae. 



