GRAITOLITES OF NEW YORK, PART 1 



595 



graptolites, were denizens of the deeper littoral regions, where they formed 

 continuous fields. 



Lapworth [J, Walther, 1897, p.250] reports that in some forms of 

 Dictyonema not only does the rhabdosome begin with a sicula, but this 

 sicula is provided with a nema, as in the Rhabdophora, and that this nema 

 persisted as a perpetual means of attachment to foreign 

 bodies or to a central network of filaments (hydror- 

 hiza) throughout the whole life of the rhabdosome. 



All specimens of D. flabelliforme, obtained 

 at Schaghticoke and in the region of Granville, which 

 retained more than the sicula, shoAved this to extend 

 into a fine nema [^see the large specimen figured on pl.l, 

 fig.20]. All the young stages, of which great numbers 

 were obtained, possessed long nemas, often extrava- 

 gantly long as in the specimen represented on the same 

 plate, figure 1, where the nema is nearly 20 times as 

 long as the sicula. In a few cases [pl.l, fig. 10] this 

 nema seems to end in a I'ather large subcircular, very thin, chitinous disk, 

 which does not show any structural features. The nema has been slightly 

 flexible, as its gentle curves prove, and it would appear to be hardly strong 

 enough to have supported the young colonies, not to speak of the full grown 

 specimens. I have, therefore, represented all these specimens as suspended. 



In assuming that the rhabdosomes of D . flabelliforme were sus- 

 pended, I am however well aware that there exist facts which apparently 

 combat such a conclusion. One of these is, in my opinion, the opening of the 

 thecae toward the inside of the basketlike rhabdosome. As the zooids were, 

 no doubt, provided with some form of prehensile organs by which they 

 caught small organisms, it would at first glance seem that in a suspended 

 colony of this kind they were in a very unfavorable condition and shut out 

 from their food supply. But it is to be considered that they may have set 

 up, by the action of their arms, a circulation which carried organisms and 

 food particles into the cone, where escape would be impossible ; and it is also 



Figr.W Dictyonema caver- 

 nosuin WIman. Proximal end 

 of rhalxJosorao, with "adhesive 

 disk." xlO (Copy from Wlman) 



