GRAPTOLITES OF NEW YORK, PART 1 571 



not irrepi'oacliable, there is little doubt that by it two groups of the 

 Graptoloidea can be distinguished, which also differ in other structural 

 features and which are separated in time. These are the Dichograptidae 

 and Diplograptidae in their ^videst sense. Freeh, however, unites under the 

 Axonolipa the Dendroidea and the Dichograptidae, two groups which, by 

 the character of their thecae and their mode of growth, appear to us too 

 widely separated to be united with propriety in one order. We have 

 for this reason, retained the original division into the orders Dendroidea 

 and Graptoloidea, and divided the latter into the suborders Graptoloidea 

 Axonolipa and Graptoloidea Axonophora. Neither of these principal 

 groups can, at present, be genetically connected with any of the others, 

 while the closer genetic relation of their subdivisions is little to be doubted. 



(1) The order Dendroidea is represented in our fauna by the family 

 Dendrograptidae with the genera Dendrograptus, Dictyonema, Desmograptus, 

 Callograptus and Ptilograptus. 



(2) The order Graptoloidea is divided into the suborders B^ Graptoloidea 

 Axonolipa and Bg Graptoloidea Axonophora. 



The suborder Graptoloidea Axonolipa comprises the provisional family, 

 Dichogi'aptidae seiisu st/>'icto, the Phyllograptidae and Coenograptidae. The 

 Dichograptidae will eventually be divided into the series of genetically 

 connected forms discussed above. For the present it seems most practical 

 to retain the old terms Clonograptus, Bryograptus, Goniograptus, Logano- 

 graptus, Dichograptus, Tetragraptus and Didymograptus. 



The small family Phyllograptidae contains but one genus, 

 Phyllograptus. 



A family, Leptograptidae, was erected by Lapworth to receive the 

 genera Coenograptus, Nemagraptus, Pleurograptus, Amphigraptus and 

 Leptograptus. Our material has demonstrated that Coenograptus 

 gracilis, the type of the genus, is derived by a new form of 

 generic value for which we have proposed the term Sigmagraptus, from a 

 Goniograptus. 



^ peculiar new tenuous tetragraptid form, here described as 



