REPORT OF THE STATE PALEONTOLOGIST 1901 583 



tration of a Cambric species published by G. F. Matthew. 1 In 

 this form the primary branches are short and evidently com- 

 posed of one theca only, while all the branches of a higher order 

 are longer and distinctly figured as consisting of several thecae. 



If we compare this species with the lower Siluric species of 

 Clonograptus or with the species of Dichograptus and Logano- 

 graptus, e. g. L. logani, where the primary and secondary 

 branches are equally short, a tendency toward a concentration 

 of the dichotomous branching in the central part of the colony 

 becomes apparent. 



The genotype of Dichograptus, D. octobrachiatus, 

 and that of Loganograptus, L . logani, are found associated 

 with Goniograptus in the Deep kill section, and occur in younger 

 specimens, which indicate that these genera also conform to 

 the composition of the internodes of one theca each. 



The denticulate nature of the branches of the first and follow- 

 ing order in Temnograptus was already known to Hall (G r . 

 m i 1 e s i Hall) and has been recognized in its related genera 

 (Holograptus, etc.). 



Holm has described a coenograptid (Pterograptus 

 e 1 e g a n s), 2 with a distinct thecal structure in the two principal 

 stems, and the writer figures (fig. 

 13) a young specimen of Coeno- 

 graptus gracilis itself, 



which distinctly shows the thecal c ^\ | | / 



structure of these stems. 



It becomes therefore probable 

 that all parts of the hydrosome of 

 the Dichograptidae, including fun- Fig-13 Coenograptug gracilis Ha ii. 



. -. , . . -, , . , „ Young hydrosome.which shows composition 



lCle and principal Stems, COnSlSt Of of funicle and principal stems of thecae. 



Normanskill shale of Mt Moreno. x4 



thecae; with the exception of the 



nema, which carries the sicula, and of the central disk. 



3 The growth stages of Goniograptus indicate that the bifur- 

 cations of the branches throughout the hydrosome take place in 



1 N. Y. acad. sei. Trans. 1895. p. 295. 



2 6fyersigt af K. Vet. Ak. Forhandl. 1881. no. 4, p. 77. 



