342 H. 0. Nicholson — GfraptoUtes in the Skiddaw Slates. 



resembles my Skiddaw Slate specimen in many respects. 1 If not the 

 same species, it is a very closely allied form, the chief difference 

 being its smaller size. Professor Lap worth also describes another 

 species from the same locality under the name of Trigonograptus 

 truncatus, 2 which in many points resembles my specimen, but it 

 cannot be identical with it, as in all the Ramsey Island specimens 

 the polypary is abruptly terminated by a straight line at its distal 

 extremity, while in the present specimen the margins are seen to 

 converge towards the distal end, and clearly meet at a point. Lastly, 

 I cannot identify my specimen with Trigonograptus lanceolatus, 

 Nich. 3 The shape of the polypary in that species, owing to the fact 

 that the margins so rapidly diverge distally, is alone sufficient to 

 separate it as a distinct species. 



II. Didymograptus v-fractus, Salter, var. volucer. Fig. 3. 



The other Graptolite to be described may be provisionally referred 

 to Didymograptus v-fractus, Salter, of which it appears to be, at 

 least, a well-marked variety. It was obtained from the Skiddaw 

 Slates at Outerside, near Keswick, and is fairly well preserved. 



The two branches of the polypary in the specimen in question 

 (Fig. 3) are very distinct. They increase very gradually in width 

 from their point of origin, and attain a maximum breadth of three 

 millimetres. 



Fig. 3. — Didymograptus v-fractus, Salter, var. volucer, of the natural size. 

 Skiddaw Slates, Outerside, near Keswick. 



The sicula in this specimen is not quite complete, but seems to 

 taper gradually to a point. From the summit of the sicula the two 

 branches of the polypary diverge, forming a basal angle of 10°, and 

 at a distance of 9 millimetres from their origin each branch is bent 

 abruptly at right angles to the sicula, so as to form a straight line. 

 The denticles, which at some parts of the polypary are well defined, 

 are slightly mucronate, and there are about 15 to the centimetre. 



It will be seen from the above description that the essentially 

 characteristic point in this specimen is the general form of the 

 polypary. The original specimen of Didymograptus v-fractus was 

 figured by Mr. Salter in a note on the Graptolites of the Skiddaw 



1 Inc. cit. supra. 2 Loc. cit. p. fi60, pi. xxxiv. figs. 9a-9d. 



3 Ann. and Mag. JST. Hist. 1869. ser. 4, vol. iv. p. 232, pi. xi. fig. 6. 



