GRAPTOLITES OF NEW YORK, PART 1 603 



[fig.8, 9]. The formation of the four primary thecae takes place in such 

 a narrow space — as it would appear, along a continuation of the sicula — 

 that, where young colonies have become compressed vertically (as in figures 

 14 and 15) usually four branches diverge from the center. These continue 

 to bifurcate quite rapidly, but in unequal distances [fig.l5-l7]. Sometimes 

 they divide again so early that a whole bundle of branches seems to pro- 

 ceed directly from the distal end of the sicula [fig.l6]. Where a rhabdo- 

 some, which has developed a little further, has been compressed obliquely, 

 so as to expose the base [fig. 19], one sees a central cross, each of the arms 

 of which divides into a bush. The dissepiments or transverse connecting 

 filaments may appear already on the branches of the second order [fig.l3], 

 but they do not become common enough to form a network till the branches 

 of the third order have formed, as shown by figure 18. 



Figures 12 and 18 demonstrate that the thecae were oriented inward 

 from the beginning of the growth of the colony. On account of this 

 arrangement they are very rarely noticeable, and it was possible for Dames 

 [1873, p.383] to conclude that only the upper free ends Avere theciferous, 

 a view which has been accepted in Zittel's handbook. In perfect rhabdo- 

 somes they are only occasionally noticeable in the laterally compressed 

 marginal branches. 



The early growth stages, before the appearance of the transverse dis- 

 sepiments, have a considerable resemblance to those of Dichograptidae, a 

 fact noticed by Matthews [1891, p.38]. This resemblance is indeed so 

 striking, for instance between the early growth stages of D. flabelli- 

 formeand Clonograptus proximatus Matth., both Cambric, that, 

 when found in the same bed, it is somewhat difiicult to separate them. 

 Matthew also states, that the first branches are formed by twice repeated 

 bifurcation. Our material would, as we have just described, rather indicate 

 a successive formation of the first branches, as there occur stages with one, 

 two, three and finally with four thecae. The resemblance to the mode of 

 branching in the Dichograptidae is hence but superficial, and can not be 

 otherwise, since there exist fundamental differences in the composition of 



