270 Dr. H. A. Nicholson on some 



half a line ; and its shape is the normal triangular one. As 

 there is good evidence amongst the Diplograptidce that the 

 broader end of the sicula forms the proximal extremity of the 

 polypary, I have figured the present form in a corresponding 

 position (figs. 2 a, 2 b). The stipe is narrow, apparently 

 from one inch to two inches in length, and about one thirtieth 

 of an inch in width opposite to the cell-mouths. The cellules 

 are long and narrow, resembling those of Monograptus Nils- 

 soni in shape, remote (about twenty in the space of an inch), 

 slightly overlapping, the cell-mouths being nearly at right 

 angles to the axis. 



Owing to the remarkable appearance presented by the 

 sicula standing nearly at right angles to the celluliferous 

 stipe, there is not any difficulty in recognizing all fragments 

 of this species in which the base is preserved. Owing also to 

 the marked manner in which the stipe originates from the 

 centre of the sicula, there is no difficulty in determining that 

 we have not to deal with a Didymograptus broken off at the 

 sicula. 



I have named the species in honour of my friend Mr. Charles 

 Lapworth, whose researches have of late years so materially 

 increased our knowledge of the structure of the Oraptolitidoe. 

 The specimens from which the above description is taken were 

 kindly placed in my hands for examination by Mr. W. K. 

 Dover, who has long been an enthusiastic collector in the 

 Skiddaw Slates. They include the remains of a great number 

 of well-preserved individuals, none of which exhibits any 

 branching, though the stipes are often so thickly crowded to- 

 gether as to render this point very difficult of observation. 



Locality and Formation. — Hodgson-How Quarry, near Por- 

 tinscale, Lower Skiddaw Slates. Apparently by no means 

 of rare occurrence. 



Genus Thamnograptus, Hall. 



Polypary composed of a central rachis or stem, giving off 

 slender alternating branchlets. Cellules unknown. A dorsal 

 " axis " (?) entering into the branchlets as well as the main 

 stem. 



Much has yet to be learnt before we can speak positively as 

 to the nature and affinities of Thamnograptus, though I think 

 there can be little doubt as to its belonging to one great group 

 with the true Graptolites. There is a possibility that the 

 branchlets are greatly elongated cellules ; but it is more pro- 

 bable that the branchlets carried the cellules in a single row 

 on one face, though at present the published evidence on this 

 subject is insufficient to establish this view. 



