a Family of Graptolites. 



17 



branches (Trichograptus, etc.). The following genera come under 

 the latter category : — 



Genus III. Trichograptus, Nicholson. 

 Hydrosoma bilaterally subsymnietrically developed. Two prin- 

 cipal branches on the celluliferous side, with a series of branchlets 

 which remain undivided. Hydrothecae of the type of Monograptus 

 Nilssoni, Barr. 



1. Trichograptus fragilis, Nich., Lapw. 

 Upper part of Skidd aw Slates, N. England. 



2. Trichograptus retroflexus (Brogger). 



Bryograptus retroflexus, Brogg. 

 Upper part of Dictyograptus-sh&les, Norway. 



Genus IV. Bryograptus, Lap worth. 

 Hydrosoma bilaterally subsymmetrical, consisting of two com- 

 posite branches, diverging at a small angle from a distinct sicula. 

 From the two principal branches composite branchlets issue at small 

 but irregular intervals. 



1. Bryograptus Kjerulfi, Lapw., Brogger. 



Graptolithus tenuis, Kjerulf. 

 Dictyograptus-skaXes, Norway. 



2. Bryograptus C'allavei, Lapw. Upper Cambrian, Shropshire. 



3. Bryograptus ramosus, Brogger. 



Lower part of the Ceratopyge-shales, Norway. A very similar 

 species in abundance in shales below the Phyllograptus-skales at 

 Christiania. 



Genus V. Pterograptus, Holm (Of v. Kongl. Yet. Akad. Forh. 



1881, p. 74). 

 The hydrosoma issues from the wide end of the sicula. On the 

 two primary branches simple secondary branches arise from a number 

 of the hydrothecae towards the apex, and these are bent alternately 

 to right and left of a plane passing through the primary branch, and 

 turn their cell-bearing side towards this plane. 



Fis:. 66. 



Fig. 6a. 



Fig;. 5. 



Fie. 4. 



Fig. 4. Pterograptus dilaceratus, sp. nov. 



Phyllograptus-shales, Galgenberg, Christiania. 

 ,, 5. Tetragraptus approximatus, Nich. 



Phyllograptus-shales, Fure, Erngerike, Norway. 

 ,, 6a. Dichograptus Sedgwickii, Salter (formation and locality as in Fig. 4.) 

 ,, 6b. Part of a branch of Fig. 6a, enlarged twice nat. size to show the form ot the 

 hydrotheca. 



DECADE III VOL. III. NO. I. ^ 



