642. NEW YORK kJTATE MUSEUM 



in having the thecae a little closer arranged, narrower and smaller and less 

 overlapping, and all branches narrower and diverging more from each 

 other at their bases. These differences, combined with the fact that 

 B. kjerulfi occurs in Europe in a much deeper horizon (Bryo- 

 graptus beds), make this fomi worthy of recognition as a separate 

 species. 



With this species the genus Bryograptua makes its last appearance in the 

 graptolite beds of New York. 



TETRAGRAPTus Salter 



The genus Tetragraptus was pioposed by Salter [1863, p.l36] for 

 forms in which "bifurcation takes place twice, the branches patent or 



48(j 



Flg.48 Tetragraptus similis Hall sp. Early tfrowth 

 stage of rhabdosome etched out of Vaglnatenkalk of 

 Oeland: n Obverse side showing sicula and tlrst theca. 

 b Reverse side showing the connecting canal. xl2 (Copies 

 from Holm) 



nearly close." Thus defined, the "genus" embraces a wide range of forms, 

 which, as noted before [p.554] belong to different phylogenetic series and have 

 closer interrelations with species of other " genera " of like compass, as 

 Didymograptus and Bryograptus, than with each other. The term, while 

 eminently useful for a temporary grouping, is but an expression for a stage 

 in the general progress of the class of graptolites and does not comprise 

 a natural group of species of the same series. The genus as usually 

 understood is hence polyphyletic ; and should be subdivided into the 

 natural groups quantivalent to a genus. The entirely different thecal 

 character of a new form, [see T . 1 e n t u s] which, under the present system. 

 atic arrangement, comes under Tetragraptus, emphasizes strikingly this 

 demand of recent graptolithology. Such a grouping has been attempted by 



