GRAPTOLITES OF NEW YORK. PART 1 515 



of liydrorhiza or adhesive threads such as the mature hydroids have. They 

 were hence, at least in these cases, firmly attached in an upright position to the 

 sea bottom or to other bodies, probably sessile seaweeds. Hence their localized 

 appearance. Other Dendroidea, as Dictyonema f labellif orrae 

 have no doubt, at least at certain stages, been suspended, as the relation of 

 their long thin nema to the large rhabdosome distinctly demonstrates [pl.l j. 

 We, hence, agree with Lapworth that the Dendroidea may have been partly 

 attached in an upright position to the sea bottom or seaweeds and partly have 

 been suspended from seaweeds. Whether any were free floating can not now 

 be established ; but the discovery among the hydroids of free floating colonies 

 or hydroid colonies actually moving independently, by the concerted action of 

 the zooids, which do not differ from the sessile ones, proves that an analogous 

 case among the Dendroidea [see Dictyonema flabelliforme, p.595l 

 may be possible. 



As to the rhabdosomes of the Graptoloidea or graptolites proper, Lap- 

 worth, Giirich, Freeh and the present writer in former publications agree that 

 they were suspended. Jaekel's argument, which he brought forward for a 

 sessile mode of life, namely that the thecae would naturally be turned upward 

 toward the food supply, can be directly used as an argument for the opposite 

 hypothesis, as the investigations of Wiman and the present writer have since 

 shown, that in the axonophorous graptolites the first theca reverses its original 

 direction, and the succeeding thecae grow backward along the nemacaulus 

 to attain this ascendant position. In regard to the Axonolipa (Dichograp- 

 tidae) Lapworth has pointed out, that, on the whole, branches change 

 their dependent position gradually into a reclined or recumbent position to 

 attain the same result. 



There remains then to be discussed only the question whether all the 

 graptolites proper or Graptoloidea were suspended from seaweeds or 

 all from a "float" of their own, or whether one part had adopted the 

 former and the other the latter mode of suspension. To shorten matters, 

 we shall begin by stating that we entertain the view that the Axonolipa 

 were suspended from seaweeds, while the later Axonophora had proceeded 



