GRAPTOLITES OF NEW YORK, PART 2 213 



It can be first stated that while the rhabdosomes in habitus and occur- 

 rence are distinctly graptolitic, there: are no appendages known from other 

 graptolites which could be compared in form to these cones. But by 

 recourse to the living 1 hydrozoans, two alternatives can be suggested, viz : 

 that they were either normal thecae of nourishing individuals or gonangia 

 (gonothecae). 



In regard to the first hypothesis it can be said that this type of thecae 

 would be more similar to the hydrothecae of the hydrozoans than any other 

 of the graptolites ; first by the basal constrictions, second by the presence of 

 the paired appendages. It has repeatedly been pointed out as an important 

 difference between the graptolites and the hydrozoans that in the latter the 

 point of communication between the hydrotheca and tube of the hydro- 

 caulus is more or less constricted and in the graptolites the theca is in unin- 

 terrupted continuous communication with the coenosarcal canal. Allman 

 [1872, p.369] has for this reason compared the thecae of the graptolites to the 

 njmatocalyces and considered the graptolites as " morphologically plumu- 

 larians in which the development of the hydrothecae had been suppressed 

 by the great development of the nematophores." When it is further 

 noticed that in general habitus also the Dendrograptidi approach more to 

 the hydrozoans than any other graptolites (as noted before by Hall, Allman, 

 Freeh and others), the possibility that this form may point the way to the 

 recent hydrozoans can not fail to suggest itself. I learn from Dr Ulrich 

 that he also, on finding the material, at once recognized its great similarity 

 to the Sertularians and its possible phylogenetic importance. 



The first hypothesis is further supported, at least apparently, by the 

 fact that while in other graptolites distinct thecae or receptacles for the 

 zooids are visible as denticles on the branches, the form bearing these 

 appendages appears to possess nothing but extremely slender, uniformly 

 thin branches with circular pits and to lack all indications of a coriiposition 

 of separate tubes such as are found in Dendrograptus and Dictyonema. 



The extreme thinness and complete compression of the branches leave 

 one unfortunately in doubt as to their internal structure, especially in regard 



