24G Bepoet oe the State Geologist. 



the rhabdosomes, if found detached, would certainly be identi- 

 fied as D. quadrimuGy onatus, Hall; and others approach D. mu- 

 cronatus, Hall. It is probable that a closer study of the colonies 

 of Diplograj)tu8 occurring in the Utica and Hudson Hiver slates 

 will necessitate a revision of the species of this genus. The 

 strangeness of the appearance of many stipes is still increased 

 by irregularly distributed aggregations of pustules which have 

 their origin in crystallizations of iron pyrite within the 



rhabdosomes. 



Addendum. 



To my regret, Wiman's important paper, '' Ueber die Grapto- 

 liten," was received too late to be given the deserved appreciation 

 in this paper. I will, however, not miss this opportunitj^ to thank 

 the author for the full reproduction of my preliminary note as well 

 as for the publication of his highly developed methods of prepara- 

 tion, which, I hope, can be applied successfully to my material. 

 Besides, the writer wishes to make a few remarks on some objec- 

 tions raised by Wiman. 



Regarding the objection to the use of the terms which Hall 

 introduced for the compound colonial stock of the DiGhograptidce 

 (called by mistake compound Monograptidce instead of compound 

 Monojprionidm)^ I think that the development of the colonial 

 stock of Diplograptus^ published in this Report, will justify the 

 application of the terms in so far as it shows that the " central 

 disc" of Dijplograptus originally lies at the sicular end of the 

 colony, for it is among the earliest outgrowths of the sicula. The 

 fact that this sicula, in later stages of growth, wanders outward, 

 away from the disc, budding thecoe between the two, is a later 

 complication which, in my opinion, does not materially affect the 

 homology of the discs of Dichograptus and Dijplograptus. In 

 case the thecae of the primary rhabdosome would not grow 

 in the direction of the initial part of the sicula, but a'vay from 

 it, as in Dichograptus^ then the primary sicula would remain 

 always at the disc; or, in other words, the disc would continue 

 to lie at the sicular end of the rhabdosome. The " central discs " 

 of Bichograptus and Diplograptus therefore are, genetically, iden- 

 tical. The difference between the two comes in when the 

 colonial stock of Diplograptus^ by means of "gonangia," pro- 

 duces new stipes, while in Dichograptidae the latter are formed 



