110 Nicholson — On Graptolites. 



few cellules in an inch, and the marked alternation of the toothed and 

 angular denticles. These characters seem to me to entitle it to rank 

 as a distinct species ; but the genus Diplograpsus is in such an 

 unsatisfactory condition, that it may eventually turn out to be a 

 variety of some previously-described species. I have included some 

 forms, in which the denticles are rounded, instead of angular, as the 

 cellules distinctly alternate, and the stipe commences in a pointed 

 radicle (see Fig. 17) ; but I doubt whether these are differences of 

 variety or specific distinctions. D. acuminatus somewhat resembles 

 GraptoUthus, {Diplograpsus) angustifolius, of Hall, but is certainly 

 distinct. It is also not unlike a species which occurs in the Skiddaw 

 Slates, and has been doubtfully referred by Mr. Salter to D. pristis. 

 Loc. — Dobbs' Linn, Duffkinnel Burn ; Garple Linn, in Dumfries- 

 shire. 



Didymograpsus anceps, n. sp. (Plate VII. Figs. 18-20.) This 

 peculiar form of Didymograpsus differs from all others with which I 

 am acquainted, in the total absence, or very rudimentary condition, 

 of the radicle or initial point. So much is this the case, that it 

 might at first sight be considered to be merely a mono-prionidian 

 Graptolite, accidentally bent ; but this supposition is negatived by 

 the fact that there occur numerous specimens, the branches of which 

 are bent at the same angle and in the same way, while the serratures 

 point in the same direction in both branches. 



The frond consists of two stipes, coming off from a point, which 

 is not, as a rule, marked by any radicle (Figs 19-20), though a 

 minute mucro is to be discovered in some specimens apparently 

 belonging to this species (Fig. 18). In these cases the mucro is 

 internal, and the cellules are on the outer or convex side of the 

 frond. Considering this as the normal position, the stipes bend 

 downwards from their origin, including between them an angle of 

 20° or thereabouts, and extending in a straight or slightly curved 

 direction for a greater or less distance. The stipes rapidly attain 

 their maximum breadth (nearly one line), retaining the same dimen- 

 tions, and showing no signs of terminating as far as seen — a length 

 of two inches being reached in the larger specimens. Cellules, 

 twenty-five to thirty in the space of an inch, their extremities 

 rounded off, and their margins strongly curved, so that the denticles 

 are separated by indentations, which are rounded at the bottom, and 

 extend about half-way across the stipe (Fgs. 18a. 20a.) Sometimes 

 there are minute pustules, or circular depressions in the centre of 

 each denticle, where it joins the body of the stipe, but this does not 

 seem to be at all constant. 



This species is very easily distinguished, both by the absence of 

 any prominent and conspicuous radicle, and by the peculiar form of 

 the cellules, in which latter respect it differs from all British species, 

 and closely resembles GraptoUthus (Didymograpsus) divaricatus, 

 Hall, which is found in the Hudson Eiver Group. Loc. — Dobbs's 

 Linn, near Moffat. 



Didymograpsus flaccidus, Hall, Sp. (Plate VII, Figs. 1 — 3.) 

 This exceedingly distinct and beautiful species appears to be iden- 



