GRAPTOLITES OF NEW YORK, PART 2 



"5 



branches finally reapproach without, however, uniting and thus terminate 

 at the central organs. This is the only hypothesis on the structure of the 

 perfect colony of a Dicranograptid known to me. 



Diligent search on my part for specimens giving clues on the structure 

 of these antisicular ends has met with very little success and the solution of 

 the problem is evidently only to be expected from the fortunate discovery 

 of perfect synrhabdosomes. With few exceptions all speci- 

 mens are distinctly broken at the antisicular extremities. 

 None have shown any protruding nemas by which they 

 could have fastened themselves to the central organs with 

 the exception of a young rhabdosome of a Dicranograptus in 

 which the biserial portion is not yet completed [see text 

 fig. 41]. This interesting specimen indicates that the growth 

 of the biserial portion of the rhabdosome took place as in 

 Diplograptus and Cltmacograptus along the nema connecting 

 the sicula with the primary disk. What, however, held the 

 rhabdosome after the completion of its first portion we do 

 not know. So much seems certain that the nema did not 

 continue into any of the branches as axis. 1 A few specimens 

 of seemingly perfect rhabdosomes of Dicranograptidae were Jr S ap?u? 1C f u"' 



cat us (Hall). Rhab- 



seen to fade out at the antisicular extremities of the branches dosomc .showing two 



successive crossings, 

 • r 1 iii 1 • i i.i • 1 r The upper branch is 



as 11 there had been the growing ends and the periderm ot partly broken away 



at the first crossing. 



the thecae not yet fully secreted. st£™££N. Y. sh or!: 



ginal in National Mil- 



A specimen of Dicranograptus furcatus [see ~ seam - Nat - s ize 

 fig. 49] deserves particular notice in this connection. This shows two 

 successive crossings of the originally spiral branches, but where the third 

 crossing would be expected the two branches lie in juxtaposition for about 

 5 mm, the slab being unfortunately broken off at that point. One end 

 shows the ventral, the other the dorsal side, and the former overlaps the 

 latter a little, thus giving the impression that the two branches were in 

 contact with their dorsal sides without coalescing and pushed a little side- 



1 See discussion of the presence of a "virgula" in the Dicranograptidae on page 102. 



