H. 0. Nicholson — Graptolites in the Skiddaw Slates. 341 



which had been previously suggested by my father, so that the 

 species now stands as Trigonograptus ensiformis, Hall, sp. 



The characters of my specimen of Trigonograpius ensiformis, Hall, 

 sp., as far as it is possible to make them out, are as follows. It is 

 the upper half of a sublanceolate diprionidian polypary, about 1^ centi- 

 metres in length. There is marked convergence of the margins 

 towards the distal extremity, but the actual tip is not seen. At its 

 widest part it measures about 3 millimetres, and its total length if 

 completed would be about 3 centimetres, if we suppose the margins 

 to converge similarly towards the base, as is shown in the entire 

 specimens figured by Hall. Running up the centre of the polypary 

 is a remarkably well-defined and absolutely straight axial line, and 

 given off from this in alternate fashion are the equally well-defined 

 hydrothecal partitions. Measured vertically there are about ten 

 hydrothecaj to the centimetre. No signs of reticulation are visible. 



The specimen which I have thus shortly described was obtained 

 in the Upper Skiddaw Slates (Ellergill Beds), from a small exposure 

 in one of the feeders of Mosedale Beck, near Troutbeck, Cumber- 

 land. It is in good preservation, and the characters included in the 

 description are readily determined. From its very peculiar sub- 

 fusiform shape alone, if for no other character, I think one may safely 

 consider it to be identical with Hall's Quebec form, which Professor 

 Lapworth has now wisely removed from the genus Retiolites. The 

 present Graptolite is clearly not referable to that genus, as no trace 

 of punctation or reticulation can be detected, but this is likewise 

 a doubtful feature in Hall's specimens, as he himself hints at the 

 possibility of separating the species as the type of a new genus. 



Ml 



Fig. 1. — The specimen of T. ensi- 

 formis, Hall, sp., described above, of 

 the natural size. Upper Skiddaw 

 Slates (Ellergill Beds), Mosedale, 

 near Troutbeck. 



Fig. 2. — The preceding Figure 

 enlarged about four times. 



The Trigonograptns ensiformis, Hall, sp., described by Professor 

 Lapworth from the Lower Arenig formation, Ramsey Island, 



