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III.—Eocene Echinoids from Sokoto

Published online by Cambridge University Press:  01 May 2009

F. A. Bather
Affiliation:
British Museum (Natural History).

Extract

It is fortunate that Captain Lelean not merely discovered these fossils at Garadimi in Sokoto, but that he had enough sense of their importance to spend some time and trouble in their collection, and that now he has generously presented them to the British Museum. The collection includes four echinoid tests, five natural casts of Mollusca, and a few rock-specimens containing Operculina and other Foraminifera. The Mollusca, so far as their state of preservation admits, have been determined by Mr. R. Bullen Newton as: 3 Lucina cf. gigantea Deshayes, 1 Voluta cf. cithara Lamarck, and 1 undetermined Gastropod. The Echinoidea were partly covered by an impure limestone closely adherent to the test. The portions not so covered were in many places considerably worn, and the calcite was split by cracks, probably due to alternations of temperature, and rendering it very difficult to follow the course of the sutures. The appearance of these and the other specimens shows clearly that they have been lying on the surface of the ground for some time, and, in fact, Captain Lelean informs me that they were not picked out of the solid rock, but from the talus at the foot of the cliff. The notable variations in the matrix of the different specimens are thus accounted for. None the less it will be seen in the sequel that all the specimens are consistent with the ascription of a Middle Eocene age to the mass of limestone from which they were derived. Of the four echinoids, two have been determined as belonging to the genus Plesiolampas and two to the genus Hemiaster.

Type
Original Articles
Copyright
Copyright © Cambridge University Press 1904

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References

page 293 note 1 In the diagnoses relative measurements are given in hundredths of the length; in the descriptions the actual measurements are given in millimetres. Here length = 36–60·5 mm. The radii and interradii are numbered on Loven's system.

page 293 note 2 The base-plane is the flat horizontal surface on which the denuded test assumes stable equilibrium in its natural posture. The anterior vertical plane is at right angles to this and to the sagittal plane, and parallel to the transversal. The height of the vertex or any other part should always be measured from the base-plane.

page 299 note 1 See footnote, p. 293. Length here = 21–32·3 mm.

page 300 note 1 Since noting the asymmetry in Hemiaster sudanensis, I have detected it in specimens of the genus from widely separated localities and horizons. It can be no mere individual abnormality.

page 300 note 2 See footnote, p. 293.

page 303 note 1 “Sur les traces de la mer lutétienne au Soudan,” C.R. Acad. Sci. Paris, cxxxvi, pp. 1118–1120; 11 May, 1903; and “Sur de nouveaux fossiles du Soudan,” tom. cit., pp. 1297–8; 2 June, 1903.

page 304 note 1 Bull. Soc. Geol. France (4), i, p. 189; 1901. See alsoDe Lapparent, A., C.R. Acad. Sci. Paris, cxxxii, p. 388; 1901.Google Scholar