604 NEW YORK STATE MUSEUM 



the branches between the Dendroidea, including Dictyonema, and the 

 Graptoloidea, to which the Dichograptidae belong. It also follows from the 

 mode of formation of thecae in D . c a v e r n o s u m , discovered by Wiman 

 [1896], that the four branches of the first order should appear successively 

 instead of in pairs; for, as the first budding individual appears together 

 with the sicula, and produces a theca, a gonangium and another budding 

 individual the last of which, again, gives origin to three different individuals, 

 these thecae must, when seen exteriorly, appear in single succession and not 

 paired ; and so must the branches. 



While our material does not exhibit the gonangia and budding 

 individuals, it indicates the presence of smaller tubiform thecae also in this 

 species, for some thecae [fig.5, 8, 9] are distinctly bipartite and tripartite, or 

 longitudinally divided, for example the middle one in figure 8. Figure 11 

 represents a partly pyritized specimen, in which the composite character of the 

 thecae becomes still more apparent. 



Wiman observed, by cutting the proximal part ofD. cavernosum, 

 figured above, into thin sections, that, as soon as this part begins to show 

 something more than the disk, there appear two individuals, namely a 

 larger theca which opens on the stem and a smaller budding individual. By 

 discussing the possible modes of origin of these two individuals, he arrives 

 at the conclusion that two of them are most probable — namely, that 

 either a free swimming, nonchitin-secreting individual became sedentary and 

 produced the two first chitin-secreting individuals, or that the theca was older 

 and produced the budding individual. Our series of growth stages of 

 D. flabelliforme, presented on plate 1, tends to demonstrate the 

 existence of a primary theca, as the inception of the colony, without any 

 adhering tube, which could represent the budding individual [fig.l]. In regard 

 to this theca Wiman states, that it is no common nourishing individual, i. e. 

 no theca in the sense used for the Dendroidea ; but for the latter an entirely 

 new kind of individual, which, if not morphologically, yet functionally, as 

 mother of but one individual, corresponds to the sicula of the Graptoloidea. 



