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III.—On the Organization and Economy of the Graptolithidæ

Published online by Cambridge University Press:  01 May 2009

Extract

In the first place, let us obtain a clear idea of a Graptolite, and for this purpose we will consider two members of the family Dichograptidæ, namely, Didymograptus vacillans, Tullb. (Fig. 2, p. 452), and Dichograptus octobrachiatus, Hall (Fig. 1, p. 449).

Type
Original Articles
Copyright
Copyright © Cambridge University Press 1885

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References

page 450 note 1 Figures and Descriptions of Canadian Organic Remains, Dec. ii., Graptolites of the Quebec Group, Montreal, 1865.

page 450 note 2 Ueber Graptolitheu, etc., Breslau, 1851.

page 450 note 3 Die Versteinerungen der Grauwackenformation in Sachsen: I. Graptolithen, p. 17

page 450 note 4 Monograph of the British Graptolitidæ, p. 63.

page 451 note 1 “On Dicellograptus, a new genus of Graptolites,” Geol. Mag. Vol. VIII. (1871), No. 1.Google Scholar

page 451 note 2 “Monograph of the British Graptolitidæ” (1872), p. 55.

page 451 note 3 “Notes on British Graptolites,” Geol. Mag. Vol. X. (1873), p. 501.Google Scholar

page 452 note 1 Monograph of the British Graptolitidæ, p. 63

page 452 note 2 “On Dicellograptus,” Geol. Mag. Vol. VIII. (1871), p. 22.Google Scholar

page 452 note 3 “On the Graptolites of the Arenig and Llandeilo Rocks of St. David's,” Quart. Journ. Geol. Soc. vol. xxxi. (1875), p. 640.Google Scholar

page 453 note 1 The question of the angle of divergence appears to me to be a comparatively simple matter. Leaving out of consideration the two sides of the branches, the angle of divergence is that formed by the axial lines of the branches at their meeting-point in the sicula. Assuming the two branches to grow quite straight out from the sicula, there will be no angle of divergence (0°), and the celluliferous margins will be in contact;—then, as the branches diverge, sweeping round the imaginary circle of which the sicula is the centre (of course in the direction of the non-celluliferous margin, as otherwise they would have to cross each other), these axial lines will form gradually increasing angles, until the dorsal margins come close together, when we get 360° as in fig. 5. Roughly speaking, the angles shown in the figures would be, for fig. 2, about 90°; fig. 3, about 270°; fig. 4, 360°, and 330°; and for fig. 5, 360°.—W. S. D.

page 455 note 1Pterograptus, ett nytt Graptolitslägte,” Öfv. Kongl. Vet. Ak. Förh. 1881, No. 4.

page 457 note 1 Geological Survey of Canada: Graptolites of the Quebec Group, Montreal, 1865, and Introduction to the Study of the Graptolites, Albany, 1868.

page 458 note 1 Ann. Mag. Nat. Hist. Jan. 1882, pp. 54–57.

page 458 note 2 Journ. Quek. Micr. Club, vol. i. p. 161.Google Scholar

page 458 note 3 Ann. Mag. Nat. Hist. Soc. ser.5, vol. ix. (1882), pp. 5457.Google Scholar

page 459 note 1 Ann. Mag. Nat. Hist. (1873), ser. 4, vol. xi., pp. 140.Google Scholar