GRAPTOLITES OF NEW YORK, PART 1 545 



graptus and Diplograptus) ; (4) tlie Tet/raprionidae witli the Fhyllograptidae 

 and the single genus Phyllograptus. 



The Retioloidea were divided into the Glossograptidae (a provisional 

 family with the genera Grlossograptus, Retiograptus and Lasiograptus) and 

 the Retiolitidae with the genera Clathrograptus, an unnamed genus for 

 Retiograptus eu char is Hall, Trigonograptus and Retiolites, 



This classification, which was supported by concise and clear generic 

 definitions, given in an analytic table, has been generally adopted and has, as 

 far as the grouping of the genera into families is concerned, thus far well 

 stood the test of later investigations, so that, on the Avhole, the families 

 appear to represent natural divisions. Lap worth himself claimed already for 

 the families of the Monoprionidae that they represent natural divisions, seeing 

 a confirmation of his claim in " the known geological distribution of the 

 genera constituting the several families." 



The investigations of Swedish paleontologists, on uncompressed material, 

 have however demonstrated that some of the larger divisions contain heter- 

 ogeneous material and that the forms constituting others are not entitled to 

 comprise a group of higher rank. The Monoprionidae contain at least two 

 widely different groups, viz the Monograptidae and the Dichograptidae. The 

 former, which are among the last appearing Graptolitidae, have in their 

 rhabdosomes proximally or inwardly directed thecae and a virgula, and 

 are derivatives of the Diplograptidae ; while the Dichograptidae, which con- 

 tain some of the earliest genera, as Clonograptus, have distally directed thecae 

 and lack a supporting rod within the branches. The division Monoprionidae 

 is hence best discarded and has in fact not been used in the latest systematic 

 arrangements, as those of Wiman and Freeh. 



The suborder Diprionidae has likewise become untenable on account of 

 the fact that the rhabdosomes of the Diplograptidae are monoprioDidian in 

 origin, i. e, originate from one theca, the consequent close relationship with 

 the Monograptidae, and the further fact that the Retioloidea contain forms 

 with a like arrangement and origin of the thecae. 



