GHAITOLITES OF NEW YORK, PART 1 



591 



membraue of attaclimeut, still otliei-s a so called disk of fixation, and others, 

 finally, are provided with a delicate filament of attachment, which (certainly 

 in the first growth stages of the rhabdosome) was as long and delicate as the 

 nema of a young graptoloid. A comparison of the specimens of D. flabel- 

 lif orme, from Schaghticoke [pl.l] and St 

 Johns, shows that these different forms of 

 attachment may even occur in the same 

 species. Lap worth is, in the writer's opinion, 

 therefore justified in holding [ibid. p. 2 5 4] 

 that, whether the nema developed into a 

 stem, a disk, a membrane or a filament, is per- 

 haps not so essential as it might appear at 

 first glance, these formations all being only 

 variations of the nema. This view is at vari- 

 ance with the suggestion of Holm that the 

 basal part of Dictyonema might supply the 

 means of a natural subdivision of the genus, 

 Avhich have not yet been found in the char- 

 actei's of the rhabdosome. 



From the appearance of the delicate, 

 fiexible nema Lapworth also concluded 

 that Dictyonema must have been suspended 

 like a bell at the end of a rope, as he supposes, from seaweeds. 



Wiman published in 1897 [p.852] an investigation of the structure of 

 some graptolites of Gotland. Among the latter he had a specimen of 

 D. cavernosum which shows two colonies apparently fastened to the 

 same stolon \see text fig. 25], and, as he concludes from his sections, also pro- 

 duced from the same hollow stolon. This discovery w^ould, if Wiman observed 

 correctly, introduce an entirely new mode of propagation of Dictyonema. 



The question suggests itself at once, whether the long nema observed 

 in the young of D. flabelliforme was not such a stolon. Such a view 

 is, however, controverted by the fact that the nema begins with an adhesive 



Fig. !i5 Dictyouema cavernosum 

 Wiman. Proximal end, showing stolons. xlO 

 (Copy from Wiman) 



