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IV.—On a new Genus of Graptolites, with Notes on Reproductive Bodies4

Published online by Cambridge University Press:  01 May 2009

Henry Alleyne Nicholson
Henry Alleyne Nicholson
Affiliation:
Baxter Scholar in the Natural Sciences in the University of Edinburgh.
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Extract

The Graptolite which I am about to consider is perhaps one of the most remarkable of all our known British forms, and was originally described by Mr. W. Carruthers, under the name of Cladograpsus linearis. The genus Cladograpsus is one which was proposed by Geinitz to include certain forms of Didymograpsus; but Mr. Carruthers seems subsequently to have seen that the reference of G. linearis to this genus was inappropriate, as he has recently alluded to it, under the title of Dendrograpsus linearis.

Type
Original Articles
Information
Geological Magazine , Volume 4 , Issue 36 , June 1867 , pp. 256 - 263
Copyright
Copyright © Cambridge University Press 1867

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Footnotes

4

Read before the Geological Society of Edinburgh, March 21s.

References

page 256 note 5 Annals and Magazine of Nat. Hist., Vol. iii. No. 13.Google Scholar

page 256 note 6 Geol. Mag., Vol. IV., No. 2, p. 70.Google Scholar

page 257 note 1 Mem. Geol. Survey, Vol. iii.Google Scholar

page 257 note 2 Hall, “Graptolites of the Quebec Group,” pp. 126, 127. Plate xvii.Google Scholar

page 258 note 1 Hall, op. cit. supra, pp. 107, 108. Plate xii.Google Scholar

page 258 note 2 Pal. New York, Vol. i. and iii.Google Scholar

page 258 note 3 Quart. Journ. Geol. Soc., Vol. xi.Google Scholar

page 258 note 4 Since the 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.

page 259 note 1 Quart. Journ. Geol. Soc., Vol. vii.Google Scholar

page 260 note 1 Op. cit. supra, Plate xvii. Fig. 3.Google Scholar

page 260 note 2 “Graptolites of the Quebec Group,” p. 33. Plate B, Figs. 6–11.Google Scholar

page 261 note 1 I altogether question the absence of the “common canal” in any true Graptolite; though Mr. W. Carruthers has recently denied that it exists as a distinct structure, referring especially to Diplograpsus pristis, His., D. folium, His., D. cometa, Gein., and Graptolites sagittarius, Linn. (Geol. Mag. Vol. IV. p. 70)Google Scholar. In this opinion Mr. Carruthers stands, I believe, alone amongst those who have written on the subject; and Hall's observations in particular appear to be almost conclusive against it. Thus Hall has shewn (“Graptolites of the Quebec group,” p. 28, pl. A, figs. 4, 5, 9) that the cell-partitions may extend to the axis, and may, nevertheless, leave room for a common canal, as in D. bicornis. The mere fact, therefore, that the cell-partitions reach the axis, as they certainly seem to do in D. folium and in D. cometa, does not justify us in asserting that there is no common canal, in the absence of sections such as those made by Hall. In the case of D. pristis and G. sagittarius I believe that Mr. Carruthers is in error, and that the cell-partitions do not really reach the axis, at any rate in full-grown specimens. In D. Pristis, His. I have observed conclusive evidence of the existence of the common canal as a distinst structure, since the axis, where prolonged beyond the distal extremity of the stipe, is in some specimens bordered by the common canal on both sides, the cellules alone being wanting, either because they have fallen off previously to fossilization, or because they had not yet been developed.

page 262 note 1 I take this opportunity of stating that I now am inclined to believe that one variety, at any rate, of the Diplograpsus tubulariformis, which I lately described from the Moffat shales (Geol. Mag., Vol. IV. p. 109, Plate VII. Figs. 12–13), is really identical with D. cometa, Geinitz, and must therefore be abandoned as a distinct species. Geinitz's description, however, and figures have been founded on imperfect specimens, and do not recognise the essential characters of the species.Google Scholar