NICHOLSON SKIDDAW GRAPTOLITES. 1J-J7 



above species, described by Hall from the Utica Slate and Hudson- 

 river Group (Caradoc). Other specimens possess broader stipes and 

 a more open angle of divergence than the true D. serratulus, Hall ; 

 but I have referred them with some hesitation to the same species, 

 since I am averse to multiplying species upon imperfect materials, and 

 the preservation of most Skiddaw-Slate Graptolites is such that 

 little more than the general form of the frond can be satisfactonly 

 made out. The only Quebec Graptolite with which this could be 

 confounded is the D. (OraptoUthus) extensiis of Hall (Grapt. Quebec 

 Group, p. 80, pi. 2. fig. 12), from which it is readily separated by 

 the greater width of the stipes and the small size of the radicle in 

 the latter. Further, the stipes diverge horizontally at an angle of 

 180° in D. extensus, but have an upward inclination in D. serratulus, 

 and never include a larger angle than 150°. Lastly, the cellules in 

 the former appear to be more closely set than in the latter. Still it 

 must be confessed that some of our specimens approach very nearly 

 to the characters of D. extensus, Hall, from which, in the bad preser- 

 vation of the cellules, they can only be separated by the fact that the 

 stipes invariably incline upwards, at any rate at their commence- 

 ment. 



In D. serratulus, Hall, including all our specimens for the present 

 under this name, the frond consists of two long and narrow stipes 

 proceeding from a long and slender radicle, and including an angle of 

 from 115° to 135°, or sometimes even 150°. Variable as the angle 

 of divergence thus seems to be, it may fairly be doubted whether 

 any stress can be laid on this character as a specific distinction. 

 The stipes are narrow at their origin, not exceeding J^- to -g-L of an 

 inch, but gradually widening out until a breadth of -^ of an inch may 

 be reached. They usually proceed in straight lines from the radicle, 

 but sometimes they present a slight backward curvature. The axis 

 is well marked, the cellules about 25 in the space of an inch, in- 

 clined to the axis at a small angle, with the cell- apertures at right 

 angles with the axis and extending about halfway across the breadth 

 of the stipe. The denticles are angular and not unlike Graptolites 

 Sagittarius, Linn., forwhich fragments might very readily be mistaken. 

 In a specimen in my possession one of the stipes shows a length of 

 more than four inches ; so that the entire frond must have attained a 

 very considerable size. 



Log. Outerside and Barff, near Keswick. 



Genus Diplogeapstjs, M'Coy. 



The genus Diplograpsus was established by Prof. M^Coy to include 

 those Graptolites which consist of two simple monoprionidian stipes 

 united by their solid axes into a simple linear frond, which is cellu- 

 liferous on the two sides. The frond is probably always furnished 

 with a radicle at the base ; and in most cases the solid axis is pro- 

 longed beyond its distal extremity. 



Whilst the generic characters of i)ijpZo^rapsi(S are thus remarkably 

 clear and unmistakeable,the specific distinctions are unusually obscure. 

 In determining the species of Diplograpsus two points are mainly to 



