598 NEW YOKK STATE MUSEUM 



disk and ends in a distinct sicula from which the rhabdosome grows, while 

 in D. cavernosum a stem containing a theca and a budding individual 

 appears to grow directly from the stolon. 



As Wiman has described similar stolonlike filaments as extending from 

 the basal disks of other Dictyonemas and the rootlets of D. flabelli- 

 f orme figured by Matthew are also distinctly dividing into filaments, it can 

 be inferred that the rhabdosome of D. flabelliforme was up to maturity 

 suspended by a thin nema from an adhesive disk [pl.l, fig.20], that it then 

 however secured — perhaps not always — a finner attachment by a secondary 

 disk or a hydrorhiza, which lay close to its sicula, as is indicated by Matthew's 

 specimens. If this disk then produced stolons from which grew new rhabdo- 

 somes, we would have rhabdosomes of two orders, those of the first order, 

 prodiiced directly from the sicula, and those of the second order, which 

 budded from the stolons of those of the first order, or a composition of the 

 entire colony somewhat analogous, but different in origin, to that foimd in 

 Diplograptus. 



Holm [1890, p.4fj has discussed the state of our knowledge of the genus 

 and specially of its species and shown that most of them have been or had to 

 be founded on insufficient material. In most cases nothing but portions of the 

 rhabdosome have been described without knowledge of the thecae. A table 

 given in the cited work shows that, of the 25 species known at that 

 time, the whole rhabdosome and the thecae in their profile view were known 

 in the case of but four. Most species are, therefore, founded only on the 

 thickness of the branches and dissepiments, the number of branches, the 

 form and dimensions of the meshes. He suspects, therefore, that not all 

 forms described as Dictyonema belong to that genus, specially as it, in 

 striking contrast to all other genera of graptolites, which are very short- 

 lived, is the first appearing and the last disappearing genus, and thus 

 Avould seem to range from the Upper Cambric into the Middle Devonic 

 Hamilton beds. The discovery of specimens embedded in limestone will 

 certainl}' furnish in time the characters necessary for a division of the genus. 

 In fact Wiman [1900, p.l89] has proposed to restrict the genus to forms 



