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III.—Contributions to the Palæontology of the Yorkshire Oolites
Published online by Cambridge University Press: 01 May 2009
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Bibliography, etc.—This somewhat insignificant fossil approaches several of the small granulated or tuberculated species of Trochus (or Monodonta), which are distinguished by a completely conical outline, resulting from a close suture and perfect flatness of the whorls. Although without description, Phillips's figure is characteristic, and it is somewhat singular that this species was not recognized by D'Orbigny amongst the fossils of the French Jurassic. The typical form is confined, in Yorkshire, so far as I know, to the Scarborough Limestone (zone 3), where it is rare, and, for the most part, so imperfectly preserved, that accurate description is a matter of some difficulty.
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page 123 note 1 This specimen is in a small tray mounted on a tablet in the Woodwardian Museum. The tablet is labelled “ Trochus, Cornbrash, Scarbro'.” The tray also contains a MS. note, apparently in the handwriting of the late Dr. Lycett, which runs thus: “ A (?) Fistulana figured by Deslongch. from the For. Marble of Langrune is probably the same as your rare Cornbrash one.” At present I have not been able to ascertain what reference is here intended. One rarely gets a fossil in such good preservation as this: hence, I have ventured to distinguish it.
page 125 note 1 On looking over the Bean Collection at the British Museum, I found a specimen of Trochus in an indurated gritty marl of a grey colour, which might be either Cornbrash or Kelloway Rock—most probably the latter. This fossil is evidently allied to the group just described (see Plate III . Fig. 5).
The spiral angle is about 65°–70°. There is no projection of the basal belt; on the contrary, the sudden increase is just below the suture, as in T. Scarburgensis. In the body-whorl the spaces between the spirals are remarkably wide, and besides the usual oblique axial striation, fine spiral lines may be noted between the more prominent spirals. A similar feature may be noted in a Trochus belonging to the Yorkshire Philosophical Society, which is either from the Cornbrash or Kelloway Rock. Shall we give these a temporary distinction as T. Scarburgensis, var. interlineatus?
page 126 note 1 There is another specimen placed on the same tablet which appears to me to represent a smaller and more coarsely ornamented species, or at any rate a well-marked variety (not figured); also from the Cornbrash. The following is the description.
The number of whorls is about 7 or 8. The angle of increase is very slightly convex, whorls nearly flat: suture very distinct. The ornaments consist of about 7 straplike spirals, slightly granulated, and separated by very narrow and shallow sulci. A raised belt with spiral lines slightly granulated terminates the flank of the body-whorl, thus constituting the basal periphery. Base flat; other indications wanting.