NICHOLSON SKIDDAW GRAPTOLITES. 141 



size until the straight portion of the stipe is reached. The soHd 

 axis would seem not to have been prolonged, in the adult, beyond 

 the distal extremity of the stipe, all apparent specimens of this 

 prolongation having probably been produced by breakage ; but this 

 is uncertain. 



On this definition the genus would include a large series of forms, 

 of which G. SedgwicJcii, Portl., G. Sagittarius, Linn., G. priodon, 

 Bronn, and G. lobiferus, M'Coy, may be taken as typical examples. 

 As already stated, Prof. James Hall denies the existence of any 

 Graptolites coming under the above definition, referring all examples 

 of such to the breakage of compound monoprionidian forms, such as 

 constitute one section of the unmanageable genus Graptolitkus, Hall. 

 This objection may possibly, and, indeed, probably, hold good as far 

 as the Quebec group is concerned ; but it breaks down entirely when 

 applied to the Graptolitic rocks of Scotland, Wales, Ireland, and the 

 Continent generally ; and it becomes impossible for us to question 

 the real existence of a group of perfect adult Graptolites with the 

 characters given above. These, then, and these only, should be in- 

 cluded under the genus Graptolites or Grajptolithus. As regards 

 the Skiddaw Slates, which contain numerous branching Graptolites, 

 I certainly am inclined to think that the genus Graptolites is not 

 represented, and that the forms originally ascribed to it are in 

 reality fragments only of the compound species. At any rate, no 

 instance has come under my notice of any specimen in which a 

 slender curved base is shown, and all the described simple Grapto- 

 lites said to occur in the Slates can be readily referred to known 

 compound forms. 



Four simple Graptolites have been described from the Skiddaw 

 Slates, viz. G. latus by Prof. M'Coy, G. Sagittarius, G. tenuis, and 

 G. Nilssoni by Mr. Salter. 



21. Gkaptolites latus, M'Coy. (Quart. Journ. Geol. Soc. vol. iv. 



p. 223, and Brit. Pal. Eoss. p. 4.) 



This name is applied to fragments of stipes, common in the Skiddaw 

 Slates, and characterized by their great width and by the triangular 

 submucronate denticles. The species appears really to have been 

 founded on portions of the stipes of Dichograpsus octobruchiatus, 

 HaU, Didymograpsus patulus, Hall, Tetragrapsus bryonoides. Hall, 

 and probably other species. While not representing a true species, 

 the name may be usefuUy retained as a convenient designation for 

 the numerous specimens which are too fragmentary to admit of 

 specific or generic determination. 



Loc. Everywhere in the Skiddaw Slate district. 



22. Graptolites sagittaeius, Linn. 



Fragments occur not infrequently in the Skiddaw Slates, which 

 certainly cannot be distinguished from portions of this species ; but 

 it is highly probable that they really belong to Dichograpsus Logani, 

 HaU, and Didymograpsus serratulus. Hall, with perhaps other forms. 



Loc. Outerside; Barff; Scawgill, &c. 



