Genus Graptolithus. 175 



branches. Some of the species have heretofore been referred to 

 that genus, and others to Gorgonia. They may be known from 

 either of these genera by the striated and serrated corneous skele- 

 ton, and absence of round ceil ides, which latter character, with a 

 calcareous frond, marks the Fenestella. 



Since the essential characters of Dictyonema, with figures of two 

 species, have been given long ago, and their similarity to Grapto- 

 lites pointed out, I am disposed to retain the name, and to describe 

 the Canadian species under that designation. 



There are still two other types in this collection which seem to 

 merit generic distinction. One of these consists of imperfect 

 branching fronds, the smaller branchlets of which are often rigidly 

 divergent from the main branch at an angle of about thirty-six 

 degrees. In others the branchlets diverge in a similar manner, 

 but are less rigid. Exterior of branches smooth, interior surface 

 celluliferous. There are two or three forms of this type which I 

 propose to designate as Dendograptus. 



Another form consists of fronds which are strong stipes near 

 the base, and become numerously and irregularly branched, end- 

 ing in a great number of filiform branchlets, one side of which is 

 serraed. The general aspect is that of a shrub or tree in minia- 

 ture. For these forms I would pi opose the generic name of Tham- 

 nograptus. 



There is also a single species approaching in character to that 

 published in the Report of the Fourth Geological District of New 

 York as Filiates ? The lateral branchlets are much longer, more 

 lax and slender, being in this respect more nearly like Filiates 

 gracilis of Shumard, (Geol. Report of Missouri, part 2, p. 208, pi. 

 a. fig. 11) but the branchlets in the Canadian species are longer 

 and more slender. They have all the same general plumose cha- 

 racter, and from the well preserved corneous structure in the Ca- 

 nadian specimens, I regar i them as belonging to the Graptolidese, 

 although the celluliferous or seriated margins have not been seen. 

 For these forms of Canada, New York and Missouri, should they 

 prove generieally identical, I propose the name of Pltjmalina, 

 making the Filicites ? cited above, the type of the genus with the 

 name of Plumalina plumaria, while the western species will re- 

 ceive the name of P. gracilis. 



The disk-like forms which are described in the Palaeontology 

 of New York, vol. 1, p. 277, under the name of Discophyllum, are 

 probably the disks of a species of Graptolithus with numerous 



