GRAPTOLITES OF NEW YORK, PART 2 225 



of C. gem mat us has apparently been also free. .Since the Dendroidea 

 to which the genus if graptolitic, must belong, were mostly sessile, it would 

 not imply a far-reaching change it some of these forms with weak branches 

 would become creeping. To the form of the thecae approximation could 

 be found in some of the other Dendroidea. Thus Dictyonema tube- 

 rosum Wiman and D en drograp tu s? bottnicus Wiman [1895, 

 pi. 12, fig. 12. 14 1 possess thecae which curve similarly abruptly and strongly 

 outward with their distal portions, but arc not almost entirely free as 

 those of Chaunograptus. The latter feature, however, is seen in forms of 

 Acanthograptus (as A. suecicus). The extremely small overlap of the 

 thecae and their strong basal contraction may well be the cause of the weak- 

 ness of the branches and the resulting adoption of a creeping mode of 

 existence ; thus that all these anomalies represent really but one. 



Their path of development can be traced to some extent if we compare 

 the oldest of the three species (C . ge mm at us) with the later Siluric 

 and Devonic forms. The first could be referred with almost equal propriety 

 to Inocaulis of which genus it would be a slender representative. The 

 stem [see text fig. 120] especially has a distinct Inocaulis-structure and the 

 branches are more regularly alternating than in the later Chaunograpti. In 

 C. no veil us the branching is still obscurely alternating and in the 

 Devonic form it is probably entirely irregular. The first was apparently 

 still entirely free, for it possesses a stronger stem, while the last two species 

 have equally thin stems and branches and probably normally sought support 

 on foreign bodies. In both the latter species the branches and stem have 

 become entirely lax and the thecae are irregularly bent forward and back- 

 ward as opportunity of attachment on the substratum was offered. 



A sicula has not been observed in any of the species. 



Chaunograptus novellus Hall 



Plate io, figure 10 ; plate n, figure 5 



Dendrograp 1 11 s (s. g. Chaunograptus) novellus Hall. Alb. Inst. Trans. 



v. 10. Abstract, p. 2. 1879 

 Dendrograptus (Chaunograptus) novellus Hall. Geol. Sur. Ind. nth 



Rep't. 1882. pi. 1, fig. i, 2 



