630 NEW YORK STATE MUSEUM 



species of Goniograptus, for it agrees in tlie zigzag form of the principal 

 stem and tlie inclination of the branches fully with that delicate Gonio- 

 graptus. The similarity is, in fact, so great that I did not hesitate at the 

 preliminary identification of the Deep kill fauna to refer the numerous 

 fragmentary branches ofG. geometricus, occurring in that locality, 

 to Thamnograptus anna [1902, p.566]. As, however, Hall 

 expressly states that the branches of his species are filiform and do not 

 show any thecae, -svhile those of G . geometricus were found to bear 

 distinct and prominent thecae, I did not feel justified to compare my mateiial 

 any longer with that species. It is however quite possible that in the type 

 specimen of Thamnogi'aptus anna the branches expose only their 

 dorsal sides and for this reason do not skow any thecae= 



LOGANOGRAPTUS Hall. 1867 



The genus Loganograptus was erected by Hall and separated from 

 the large generic group Dichograptus Salter for the reception of the single 

 species Graptolithus logani Hall, and described [1867, p. 226] by 

 its author as being characterized by having its " polypary consisting of 

 more than eight simple stipes proceeding from a single axis, with a distinct 

 broad corneous disc." The genus is well defined and readily distinguished 

 from the multiramous Clonograpti by its " simple stipes," resulting from the 

 concentration of the dichotomy in the proximal region, and by the secondary 

 disk. It is however connected by transitions so closely with Dichograptus 

 s. st/)\ as represented by Dichograptus octo brae hiatus, that 

 these two groups have been united by several authors (Herrmann, Freeh) 

 under Dichograptus. 



But as each of these genera represents characteristic and important 

 phylogenetic stages, which require recognition, they are retained here. 

 Dichogi'aptus s. str. marks that stage in the phylogenetic series leading 

 from the multiramous forms to Tetragraptus, where the decline in the power 

 of dichotomy has proceeded so far that branches of three orders only can 

 be produced, the highest possible number of branches being then eight ; 



