I96 NEW YORK STATE MUSEUM 



principal branches longer, narrower, and less rigid and regular and more 

 hairy rootlike processes occur. 



Horizon and locality. Ten specimens (including two in Spencer collec- 

 tion labeled Inocaulis w a 1 k e r i and I . pi u m u 1 o s a ) from N iagara 

 formation and Niagara chert, Hamilton, Ontario. 



This species can be told by the distinct and numerous " denticles " 

 on both sides of stem and branches, finer and less blunt dentate than in 

 A . g r a n t i. 



Gurley refers this form, we believe correctly, to Acanthograptus [see 

 his note under Acanthograptus, p. 192]. 



One of our specimens [pi. 6, fig. 1] recalls I. divaricatus Hall 

 in its wide open mode of branching. The latter, also a Niagaran species, 

 is, however, described as being 2 mm wide — and hence probably a coarser 

 form — and as lacking the "projecting imbricating scales." The correct- 

 ness of the latter statement is made doubtful by the original drawing, which 

 distinctly shows the " scales " on the right hand branch. 



cactograptus o'en. now 



Etymology. Kaxm?, a prickly plant ; ypd<pm, I write. 



A form from the Clinton shales above the lower iron ore bed at 

 Clinton N. Y., suggests at first sight both Acanthograptus and Inocaulis, 

 the former by its prominent "spines," the latter by the broad, little con- 

 sistent appearance of the branches, but is found by closer study to differ so 

 materially from both that it can not be properly placed with either. Its 

 principal difference from both rests in the character of the "spines," which 

 as a comparison of the enlargements of the genotype [see text fig. 99] with 

 those of the genera here adduced will show are not finger-shaped and bear- 

 ing apertures on all sides as in Acanthograptus and Inocaulis, but tubular, 

 bluntly triangle in outline and of the form of large, simple thecae or " denti- 

 cles." They possess a straight, obliquely ascending ventral or outer margin 

 and a concave upper or apertural margin. These denticles have the form 

 of those of species of Dendrograptus and Dictyonema, from which genera 

 the habitus is, however, widely different. The broad middle portion of 



