258 Nicholson — On Graptolites. 



branching Graptolites, is of itself sufficiently important to constitute 

 a generic character, and a distinction of equal weight is found in the 

 mode of branching. The compound Graptolites of the Quebec group 

 either radiate from a central, non-celluliferous, branching funicle, as 

 in Dichograpsiis, Tetragrapsus, and Betiograpsus, or divide repeatedly 

 from a basal, non-celluliferous stem, or foot-stalk, as in Dendro- 

 grapsus and Callograpsus. The only Quebec species which show any 

 affinity to the genus Pleurograpsus, as above defined, are Graptolithis 

 BicJiardsoni, and G. ramuliis,^ which are placed by Hall in his ex- 

 tremely comprehensive and ill-defined genus GraptoMms. It is 

 very possible that these might, with propriety, be grouped under 

 Pleurograpsus ; but such an arrangement would at present be pre- 

 mature, as they are only known in part. Leaving the Skiddaw and 

 Quebec group, one branching complex form alone remains for 

 consideration, and this— the GraptolWius gracilis of Hall— is found 

 in the Utica state of America.^ This small but beautiful Graptolite 

 has lately been recognised in Ireland, and I am informed by Professor 

 Harkness that it is probably identical with the Bastrites Barrandi, 

 described by himself from the Dumfriesshire shales.^ It should form 

 the type of a new genus, and is at once distinguished from Pleuro- 

 grapsus by the possession of a non-celluliferous stem, or " funicle," 

 from which celluliferous branches are given off with perfect regularity 

 and on a definite plan. 



The genus Pleurograpsus cannot at present be asserted to contain 

 more than a single species, viz., P. linearis; some specimens are 

 more robust in their habit than others, and some, as I have said, 

 sub-divide more than once ; but I think these should be considered 

 as mere varieties.* 



Pleurograpsus linearis, Carruthers sp., Spec. C%ar.— Frond spreading and com- 

 pound, consisting of two stipes diverging usually from a long and slender radicle, and 

 giving origin to primary, and sometimes secondary, branches in the manner described 

 under the genus. Both the main stipes and the branches are monoprionidian, narrow 

 at their origin, and gradually widening out, till a breadth of nearly one-twentieth of 

 an inch may be attained. The main stipes appear to terminate by curving upwards 

 in the manner of a branch. Solid axis usually invisible, or seenaing sometimes to 

 exist as an impressed line along the back of the stipe. Common canal well marked, 

 about half the breadth of the stipe. Cellules eighteen to twenty in the space of an 

 inch, narrow, inclined to the direction of the axis at a very small angle. Denticles 

 remote, angular, projecting slightly beyond the margin of the stipe ; their upper 

 margins at right angles to the axis, and extending about half-way across the breadth 

 of the stipe (Plate XI. Figs. L-4). 



ioc— Hart Fell and Glenkiln Bum, in Dumfriesshire. 



The length of this beautiful and very remarkable Graptolite appears 

 to have been almost indefinite, and Mr. Carruthers states (op. cit. 

 supra) that he has succeeded in tracing one specimen for nearly 

 three feet. In connection with this species I have observed a very 



1 Hall, op. cit. supra, pp. 107, 108. Plate xii. 



! Pal- New York, Vol. i. and iii, 3 Quart. Joum. Geol. Soc, Vol. xi. 



* Smcethe above was written I have come across a small Graptolite in the Skiddaw 

 slates, which I think is referable to the genus Pleurograpsus. I shall, however, 

 reserve the description of this species for the present, as belonging more properly to 

 a paper, which I am preparing, on the Graptolites of the Skiddaw series. 



