GRAPTOLITES OF NEW YORK, PART 2 I 73 



The chief peculiarity of this genus is afforded by the character of the 

 stem, which is identical in every respect with the main branches, and, like 

 them, is denticulate or polypiferous throughout the whole of its extent. It 

 commences proximally in a flattened expansion, with irregular or frayed out 

 edges, possibly the remains of a disk or bulb of attachment. 



The mode of branching is rigidly dichotomous, the first two branches 

 being formed by the subdivision of the main stem itself. Each arm branches 

 and rebranches again and again in the same manner, at frequent and close 

 intervals, composing an elegant cyathiform or fanlike polypary, very sym- 

 metrical in form. The branches retain their original width to their final 

 division, which gives rise to two minute branches less than one tenth of an 

 inch in length. 



The hydrothecae are more prominent than those upon Dictyonema. 

 The distal extremity of each appears to have been free and slightly intro- 

 verted, as in the majority of the bilateral family of the Dicranograptidae. 



Odontocaulis is separated from Dictyonema by the absence of the trans- 

 verse dissepiments, and by the polypiferous character of the stem. From 

 Callograptus, which it much resembles, the same features effectually dis- 

 tinguish it. In Dendrograptus the stem is stout and devoid of polyps, 

 while the branches are irregularly disposed ; in the present genus the stem 

 is.no thicker than the branches, is polypiferous, and the branches are regu- 

 larly and symmetrically subdivided. It has probably its nearest ally in 

 Rhizograptus [Spencer, Canadian Naturalist, 1879, P-4^o] ; but in that 

 genus the stem appears to be barren, and the branches are possibly united 

 at intervals. 



Dr Gurley remarks on Odontocaulis in his manuscript : 



This genus was thus established by Lapworth for forms which virtually 

 combined two characters: (1) Absence of dissepiments, and (2) a polypif- 

 erous stem. Its only distinctions from Dictyonema and Callograptus lay in 

 these two features. But in O. occidentalis we find dissepiments 

 along with the polypiferous stem. Whence there is now no generic dis- 

 tinction whatever between these two Odontocaulis species and the Callo- 

 graptus species at the same horizon, except the single one of the thecae on 

 the stem. But it is not at all improbable that this is merely a question of 

 better preservation, well preserved stems being thecate. At least, of the 

 two specimens of O. occidentalis, both showing the stem, one shows thecae 

 perfectly, the other only very obscurely. 



Having said this, however, a contingency may properly be noted. 

 May it be possible that all the Callograpti at this horizon have thecate 

 stems (in other words, all be referable to Odontocaulis) ? There is, I 

 think, some ground for such a surmise. As Holm has said for Dictyonema, 

 so now for Callograptus, the very great geologic range of the genus is a 



