GRAPTOLITES OF NEW YORK, PART 2 



! 93 



we have stated before, of phylogenetic importance and expressive of the 

 relative development of the species. It has been utilized in the Mono- 

 graph of British Graptolites for the distinction of four 

 minor groups, all of which are represented in our fauna. 

 By adopting this scheme of subdivision, we obtain the 

 following arrangement of our species : 



i Dicellograpti in which the thecae have 

 straight ventral walls and horizontal apertures. 



Type. Die. complanatus Die. eomplanatus 



D. mensurans 



2 Dicellograpti in which the thecae have 

 approximately straight ventral walls, but slightly intro- 

 verted apertural portions. 



Type. Die. divaricatus Die. divaricatus 



var. bicurvatus 

 var. salopiensis 

 var. rigidus 

 var. rectus 

 D. intortus 



3 Dicellograpti in which the thecae narrow 

 aperturally, have gently curved ventral walls, and slightly 



Fig. 207 Dicellograp- 



introverted apertural portions. Vi 5 * n ^' e ?l Nic , ho ' son - 



1 r fragment of branch show- 



ing simple form of thecae 

 T\pe. Die. patllloSUS D. gurleyi and "pynform reinforce- 



-s l o J merits' of inner margins of 



■p-. 'ii ■ I'll i 1 thecal walls. (Copy from 



4 Dicellograpti in which the thecae have p«»«) 

 markedly curved ventral walls and strongly introverted and introtorted 

 apertural portions. 



Type. Die. morrisi D. sextans 



var. exilis 



var. perexilis 



var. tortus 

 D. moffatensis var. alabamensis 

 D. elegans 

 D. smithi 



