46 



The cellules number about thirty-four to the inch ; in some cases 

 they are slightly curved, and they are generally furnished with 

 slender spines, which project from their lower lips (Fig. 17). 



The fossil remains of P. typus appear on the stone as simple 

 leaf-like forms, two stipes being usually pressed together on each 

 side, but in some rare instances they have been found showing two 

 stipes in a horizontal, and two in a vertical position. 



P. angustifolius resembles P. typus in general structure, but the 

 stipes are narrower and more elongated. They also differ from 

 P. typus in being broadest near the base, from which they expand 

 rapidly until they attain their greatest width, and then taper very 

 gradually towards the distal end. The mouths of the cellules are 

 furnished with long slender spines, which curve towards the base. 



The genus Phyllograptiis is exclusively confined to the Skiddaw 

 Slates in Britain, and to the Quebec Group in Canada. 



The section Dendroidea embraces forms that are branching 

 and plant-like in their structure, and it is doubtful whether or not 

 they ought to be regarded as true Graptolites. Professor Nichol- 

 son, in his "British Graptolitidae," has tabulated one species as 

 occurring in the Skiddaw Slates, namely, Dendrograptus hallianus. 

 It is exceedingly plant-like in form, the branches spring from a 

 parent stem, and are divided and subdivided until it assumes the 

 appearance of a miniature tree. Both branches and branchlets 

 are celluliferous on one side, but unlike the true Graptolites, they 

 do not show any trace of an axis, while the parent stem is furnished 

 with a distinct root-bulb, which renders it more than probable that 

 they were fixed to the bottom of the sea (Fig. 18). 



Section Incert^ Sedis embraces forms consisting of straight or 

 slightly winding stipes, from which branches spring alternately on 

 each side. Both main stipe and branches show a central depressed 

 line representing an axis, but there is no trace of cellules. None 

 of the members of this section were known to occur in the Skiddaw 

 Slates until 1875, when Mr. Dover found one that has been figured 

 and named Thamnograptus doveri. It consists of a slightly un- 

 dulating central stipe, giving off lateral branches on each side. It 



