Hostname: page-component-848d4c4894-tn8tq Total loading time: 0 Render date: 2024-06-17T00:11:11.806Z Has data issue: false hasContentIssue false
  • English
  • Français

Rhabdocrinus n.g. from the Scottish Carboniferous Limestone

Published online by Cambridge University Press:  01 May 2009

James Wright
Get access Rights & Permissions [Opens in a new window]

Extract

When describing the Scottish species Poteriocrinus scotocarbonarius, doubts were expressed about the propriety of assigning it to Poteriocrinus (Wright, 1937, p. 402, 1939–40, p. 17). Before creating a new genus, however, it was considered desirable to make an examination of one of the chief figured specimens of the genotype species P. crassus Miller and to compare it with P. plicatus Austin. Up to the present it has not been possible to do this, and such an outcome seems unlikely for some time to come. In view of the great amount of work that has been done on this and allied genera in recent years, it is now reasonably certain that our Scottish forms are quite distinct from any English or American species or genera hitherto described. Hence the new genus Rhabdocrinus now proposed. The name Poteriocrinus is now discarded in favour of the original Poteriocrinites (Bassler, 1938, Moore and Laudon, 1943). The genotype species was described by Miller in 1821. The specimen illustrated by him as fig. 1 on the plate opposite p. 69 is intended to portray a complete cup apparently from the right posterior side. It has a few columnals attached. According to this figure the radials have horseshoe-shaped facets. The Austins state that this figure is a restoration, and they give an illustration of the same specimen from the same position (Austin, T. and T., 1843–7, pi. 8, fig. 3c, p. 74). Here also the radial facets are not well shown. There is accordingly still a slight doubt regarding these structures on this specimen. On Miller's plate, however, are several figures of detached radials and on the plate opposite p. 67 is a diagrammatic representation of the complete cup of P. crassus. All these figures show radials with horseshoe-shaped facets and a distinct articulating cross ridge, the facets themselves only occupying part of the upper surface of the radials. This type of structure is taken as typical of the genus Poteriocrinites. In the new genus now proposed the facets are quite different in shape and occupy nearly all the upper surfaces of the radials with no trace whatsoever of a cross ridge. The pattern of the surfaces in fact consists of a series of fine crenulations or striations which cross the facets in a transverse direction, i.e. from front to back. In addition, some facets are characterized by little pustules and prominences which are more commonly observed near the centre and towards the back or interior surface of the facets. These features constitute the chief distinguishing character of the new genus. As to the family to which Rhabdocrinus should be assigned, it clearly does not belong to the Poteriocrinitidae as now defined (Moore and Laudon, 1943, p. 54, fig. 5), and since it is impossible under prevailing conditions to trace any known family to which it can be referred, the matter is left open at present.

Type
Articles
Information
Geological Magazine , Volume 81 , Issue 6 , December 1944 , pp. 266 - 271
Copyright
Copyright © Cambridge University Press 1944

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

REFERENCES

Austin, T. and T., , 1843–1847. A Monograph on Recent and Fossil Crinoidea, 1–128, pls. i-xvi, London and Bristol.Google Scholar
Bassler, R. S., 1938. Pelmatozoa Palaeozoica, Fossilium Catalogus, Graven-hage, Animalia, i, 194.Google Scholar
Grenfell, J. G., 1876. Notes on Carboniferous Encrinites from Clifton and Lancashire, Bristol Nat. Soc. Proc., i, pt. 3, 471–488, pls. vi, vii.Google Scholar
de Koninck, L. G., and Le Hon, H., 1854. Recherches sur les Crinoides du Terrain de la Belgique, Mem. Acad. Roy. de Beige., 1–208, pls. i-vii.Google Scholar
Miller, J., 1821. A Natural History of the Crinoidea. Bristol.Google Scholar
Moore, R. C., and Laudon, R., 1941. Symbols for Crinoid Parts, Journ. Palaeontology, 15, 412–423.Google Scholar
Moore, R. C., and Laudon, R., 1943. Evolution and Classification of Palaeozoic Crinoids, Geol. Soc. America, Special Papers, No. 46, 1–153, 18 figs., 14 pls.Google Scholar
Sladen, W. P., 1878. On the Genus Poteriocrinus and Allied Forms, Geol. and Polytech. Soc. West Riding Yorks., vi, 242–253, pl. x.Google Scholar
Springer, F., 1911. Some New American Fossil Crinoids. Mem. Mus. Comp. Zool. Harvard, Cambridge, U.S.A., 117–161, pls. i-vi.Google Scholar
Wright, J., 1937. Scottish Carboniferous Crinoids, Geol. Mag., lxxiv, 385–410, pls. xiii-xvi.CrossRefGoogle Scholar
Wright, J., 1939–1940. The Scottish Carboniferous Crinoidea, Trans. Roy. Soc. Edin., lx, pt. 1, No. 1, 1–78, pls. i-xii.Google Scholar