GRAPTOLITES OF NEW YORK, PART 2 gg 



dosomes found [see pi. 24, fig. 5] nearly all rhabdosomes, — the mature 

 ones included — -are closely attached to the center by but very short free 

 nemacauli, the slabs are covered with other, broken-off rhabdosomes with 

 extremely long free nemacauli. This indicates that in that species the dif- 

 ferent lengths of the nemacauli may have provided space for all new grow- 

 ing rhabdosomes in the desired approximately vertical position, the oldest 

 rhabdosomes keeping ahead of the younger generations by continuous 

 prolongation of their nemacauli. 



In the two species here mentioned on account of the concavo-convex 

 sections of their rhabdosomes, none or but very short free nemacauli arc 

 observable — a very striking fact in the multitude of specimens of C. 

 typical is; it is, hence, probable that in these species the older rhabdo- 

 somes continued to hug the center of the synrhabdosome, whereby the; 

 younger generations were driven to more horizontal positions. 



The present writer has always held that the solid rod (virgula) in Dip- 

 lograptus (and probably in all the other Axonolipa) not only extended 

 through the rhabdosome but also the full length of the nemacaulus. In 

 merely suspended rhabdosomes there would be no need for this strengthen- 

 ing rod, but it is quite in line with the observation here recorded that the 

 virgula should have developed with the necessity of keeping the multiplying 

 rhabdosomes from crowding around the vertical axis of the synrhabdosomes 

 and maintaining them in more or less horizontal positions, a task that grew 

 more difficult as the rhabdosomes became longer and heavier 



g Different preservation facies of graptolites (Gurley) 1 



The difference in the aspect of the same species of graptolite in 

 different states of compression and preservation is very great, and the 



' Professor Lapworth has in his manuscript report on graptolites forwarded to 

 I)r Gurley in 1890 commented upon the great variety of appearances of Diplograptus 

 f oliaceus according to the direction of compression, kind of matrix, etc. Dr Gurley 

 has taken up this theme and worked out the various possible aspects and their explana- 

 tions; and this chapter as bearing on the deceptive appearances of all the Diplograptids 

 here described, is inserted in the general part of the memoir. 



