Nicholson — On Graptoliies. 257 



species — the Dendrograpsus fiircatida of Salter — occurring in rocks 

 of this age in Wales.' The generic characters of Bendrograpsus are 

 the possession of a strong foot-stalk, sub-dividing more or less 

 dichotomously into numerous branches and branchlets, which are but 

 slightly divergent. Neither the main stem nor the primary branches 

 are celluliferous, and the whole forms a '•' broad, spreading, shrub-like 

 frond." ^ Dendrograpsus, in fact, more nearly approaches in external 

 appearance to some of the Hydroid polypes of our own seas than, 

 perhaps, any other of the true Graptolites. In referring G. linearis 

 to Dendrograpsus, Mr. Carruthers appears hardly to have appreciated 

 its peculiar and perfectly unique character, and an examination of a 

 large number of specimens has led me to the conclusion that it 

 cannot possibly be ranged with any genus yet described, but that it 

 must be considered as constituting the type of a new genus, which I 

 propose to term Pleurograpsiis, and of which the following are the 

 generic characters : — 



Pleurograpsus, gen. nov. (Plate XI. Figs. 1-5). — Entire frond consisting of two 

 celluliferous stipes, diverging horizontally, or nearly so, from a common point (wliich 

 is usually radiculate), and giving oif branches at uncertain intervals, sometimes from 

 one side, and sometimes from the other, with an irregular alternation. Both the 

 main stem and the branches are uni-serrate, or monoprionidian. Branches coming 

 off, usually, nearly at right angles, extending for a considerable distance, and some- 

 times giving off secondary branches, in a manner strictly analogous to that seen in 

 the parent stipes. 



If we imagine a long Bidytnograpsus, such as B. Jlaccidus, Hall, extended into a 

 straight line, and giving off branches from both sides nearly at right angles, these in 

 some cases again, and similarly, sub-dividing, we shall have some idea of the general 

 plan of Fleurograpsus. The existence of secondary branches seems not to have been 

 noticed by Mr. Carruthers ; but, though rare, I have observed them in a well-marked 

 form in more than one specimen. Even tertiary branches may possibly exist, though 

 I have never seen any traces of them. The parent stipes diverge from an initial 

 point, round which the parts of the frond are grouped with something like bi-lateral 

 symmetry, and which is usually marked by a long and slender radicle (Fig. 2). The 

 radicle is, however, not infrequently absent or inconspicuous (Fig. 3), when the 

 base of the organism is only to be detected by the existence in the main stipe of a 

 point, from which the denticles are given off in different directions. The absence or 

 presence of the radicle is not, however, a matter of generic importance. 



From the description I have given it will be evident that Pleuro- 

 grapsus presents us with a compound Graptolite, branching in a 

 manner totally distinct from that known in the complex ramose 

 species of the Skiddaw slates and Quebec group, and equally different 

 from any hitherto described species from other formations. The 

 essential point of distinction lies in this, that in all the genera of the 

 branching Graptolites yet described, (with the exception of the Bidy- 

 mograpsi), there is a non-celluliferous stem — the "funicle" of Hall — 

 of which the celluliferous branches are secondary or, rarely, primary 

 offsets. In Pleurograpsus, on the other hand, the primitive parent 

 stem is itself celluliferous, and is therefore functionally distinct from 

 the " funicle," as defined by Hall ; the latter, if represented at all, 

 finding a rudimentary homologue in the radicle of Pleurograpsus. 

 This total absence of the funicle in Pleurograpsus, alone of all the 



1 Mem. Geol. Survey, Vol. iii. 

 2 Hall, " Graptolites of the Quebec Group," pp. 126, 127. Plate xvii, 



VOL. lY. — NO. XXXVI. 17 



