STUDY OF THE GRAPTOLITES. 227 



g. Polypary consisting of two simple stipes from an initial point, with a 

 single range of cellules on the outer margin of each ; or, with the 

 stipes simple for a short distance above their origin with a double 

 range of cellules, and bifurcating above with a single range on each 

 division [Didymograptus, M'CoY, in part; Cladograptiis^ Geinitz, 

 in i^B,Yt:=:DicranograptuSj Hall). 



G. arundinaceus , furcatus, sextans, 



divaricatus, ramosus, 



It will be seen that the G. clintoni of the Clinton group is the only 

 known American species of graptolite of the monoprionidian type in which 

 we have not demonstrated a more or less compound structure. It is pos- 

 sible that this species may grow in simple linear stipes as represented in 

 some of the European species; but if this should be proved regarding it, 

 such a character, taken in connexion with the peculiar form of cellules, 

 would entitle it to rank as a subgenus at least. 



