GRAPTOLITES OF NEW YORK, PART 1 527 



single theca, which, however, as Wiman's sections of rhabdosoraes of other 

 species of Dictyonema would suggest, is probably of a composite nature and 

 consists of a nourishing individual and a budding individual. It thus repre- 

 sents already a branch. This first branch diverges at an approximately 

 right angle from the sicula. Several more buds of thecal appearance and 

 apparently composite nature originate in succession, one from the other, all 

 arranging themselves around and close to the sicula, thus producing a whorl 

 of branches radiating from the apertural part of the sicula [pl.l, fig.l3, 15J. 

 These branches of the first order at once give origin by dichotomy to 

 branches of a higher order, which continue the same process. Thus is 

 produced the multitude of straight branches, which, growing downward 

 and outward, arrange themselves on the surface of an imaginary bell. 



With the astogenetic development of a muUiramous colony of the 

 cujconolipous Graptoloidea, we have become acquainted by the matei-ial of 

 Groniograptus thureaui from the Deep kill. The astogenetic series 

 of this form has been described in the New York State Museum bulletin 

 52 ; and is more fully treated in this memoir under that species [p.621 and 

 pl.6]. It represents a type of development different from that of 

 Dictyonema flabelliforme in several features, while it can be said 

 to be typical of the whole mass of Dichograptidae. 



From the sicula a single theca buds, which is noncomposite and turns 

 to one side in a horizontal direction. From this theca originates a second 

 theca, which, falling into the same line with the first theca, turns in oppo- 

 site direction. These first two thecae form the crossbar at the center of 

 all the dichograptid rhabdosomes, which has been termed the " funicle " 

 by Hall, and which hence is composed of thecae like the rest of the 

 colony. 



Both of the first two thecae divide again dichotomously, producing thus 

 four branches of the second order, which repeat the same process, the result 

 being eight branches of the third order. 



After this stage is reached, in one half of the branches the thecae 

 adopt a serial arrangement these becoming the " denticulate " branches of 



