GRAPTOLITES OF NEW YORK, PART 2 147 



PTILOQRAPTUS Hall 



We have already noted this genus in part i of this work [Mem. 7, 

 p. 587] on the occasion of the description of three species from the Deepkill 

 shales. We add here two more species which differ so markedly in the 

 character of their thecae as to invite further remarks. 



Wiman described in 1895 [p.63] the internal structure of a form that 

 he referred to Ptilograptus (P. suecicus). This welcome information 

 on Ptilograptus has been withdrawn, the species now being apparently 

 quite correctly placed by the same author under Inocaulis [1900, p. 191 |. 



That the genus Ptilograptus which now again is based only on the 

 plumose arrangement of its branches, has as complex an internal structure 

 as has been found in other Dendroidea that have been studied by means 

 of etched specimens, is quite evident from several facts, as the distinct 

 presence of pores, other than the apertures of the large thecae [see text 

 fig. 53 I and the fibrous and ropelike appearance of the branches of others 

 [see Pocta's P. glome rat us and P. ram ale].' 



Ptilograptus, as now defined by the habitus of the rhabdosome alone, 

 comprises quite obviously two different groups of forms, the same as 

 Dendrograptus [see Mem. 7, p . 5 7 8 | , viz, those with smooth branches and 

 impressed thecal apertures and those with prominent " denticles." The 

 former is characteristically represented by the genotype, P . p 1 u m o s u s, 

 and the Bohemian forms, the latter by the species here described and 

 by P. acutus Hopkinson. That this difference in external character is 

 indicative of fundamentally distinct structures is shown by the writer in this 

 memoir in the cases of Dendrograptus s. str. and Mastigograptus. 



The first of the species here described possesses in the tonguelike 

 processes of the apertures, a feature distinguishing it from all its congeners. 

 These have a similar form and like position as the dissepiments of cer- 

 tain Dictyonemas (e. g. D. cervicorne and D. cavernosum). 

 Whether they actually served as dissepiments thereby making of the pretty 



'This and other species of Ptilograptus, described by Pocta [1894] were unfortunately 

 overlooked by the writer in commenting on the species of that genus in Memoir 7. 



