Vol. L., Part I, 1939. Pages 101-104.]

Uintacrinus westfalicus (Schlüter)
in the Yorkshire Senonian.


[Received in February, 1938.]

[Read in abstract 3rd February, 1939.]

ARTICULATED specimens of the Cretaceous crinoid Uintacrinus are amongst the rarest British fossils. They have previously been recorded from the Senonian of Kent[1] and Sussex.[2] Specimens have recently been found in the only well-weathered exposure in Yorkshire of Rowe’s Uintacrinus sub-zone of the Marsupites zone, namely, the cliffs immediately north of Danes’ Dyke ravine on Flamborough Head, where the genus is represented by abundant ossicles. These are frequently in clusters suggestive of common origin in a single individual whose loose articulation has led to a complete dissociation of its component plates. Very rarely it happens that dissociation is incomplete so that the specimen retains thecal or brachial structure. It is the purpose of this paper to describe and figure some of these rarities recently collected in the above locality. As yet there is no record of Uintacrinus in the Chalk to the south of Danes’ Dyke, but from this point northwards to the limit of the Marsupites zone (as defined by Rowe) ossicles may be collected. The ossicle structure of four specimens will be described briefly and a comparison then made with specimens previously described from the Uinta Mountains and from Westphalia.

Description of Specimens.

Specimen A. Now in the collection of the Geological Survey Museum. A small cup showing the base, flattened, and some of the brachial elements, the latter slightly disarticulated by pressure. (Pl. 10).

Centrale and Infrabasals absent.

Basals. Four of the original five remain.

Radials. The original ring of five plates remains. Two are 8-sided, one 7-sided, the fourth obscured and the fifth fractured.

IBr1. Two remain, both 5-sided.
IBr2. Two remain, both fractured, but one apparently 6-sided.

In the single ray whose structure is preserved ossicles IIBr1, 2, 3, 4 are seen in each half.

Outer pinnulation commencing at IIBr2 is seen at one point.

Supplemental Plates.
Numerous interbrachials are present and there are indications that ten of these irregular ossicles composed a single interbrachial area.

A single interdistichal remains.


The diameter of the radial ring of this specimen is 1.4 cm., a trifle larger than the specimen in the Sedgwick Museum figured and described by A. G. Brighton.[3] It is noticeable in these two small specimens that the plates tend to be rounded with ill-defined edges and angles. This seems to be on indication of immaturity as in the specimen next to be described the ossicles are strongly polygonal, as are any large ossicles found singly at the Danes’ Dyke locality.

Specimen B. Now in the collection of the British Museum of Natural History (E 26234). Approximately one-fifth of a dorsal cup, i.e., one complete ray, exquisitely preserved. The radials are only a little smaller than the largest single radial yet collected by the writer, which seems to indicate the almost complete maturity of the individual preserved. (Pl. 11 & 12).

Centrale and Infrabasals absent.

Basals absent, but prominent cusps on the radials indicate that they were shield-shaped and formed a five-pointed star.

Radials. Two are preserved, and on account of the cusps mentioned above bear a fan-shaped appearance. Both are 7-sided.

IBr1. Two present, both 5-sided.
IBr2. Two present, both 6-sided.

The remaining brachial elements are seen in one ray only and are as follows:

IIBr1, 2, 3, 4 in the right-hand half, IIBr1, 2, 3, 4, 5 in the left. Also scattered ossicles from the ray to the left of the one preserved, probably IIBr2 and 3.

Outer commences at IIBr2, inner at IIBr4.

Supplemental Plates.
There are eight ossicles in each of the interbrachial areas shown. A pair of interdistichals occupies the space between the right and left halves of the ray and the inside pinnules.

The diameter of the radial ring is estimated at 1.8 cm.

Specimen C. From the Wright collection. (Pl. 13).
This shows two series of brachials associated with three large radials and other thecal plates. One portion consists of the succession IIBr1, 2, 3, , 5, 6, 7, 8, 9, 10 with outer pinnulation apparent at IIBr2 and 5. The other arm-section consists of ten secundibrachs, probably commencing at IIBr1, which is fractured.

The mean breadth of ossicles remains fairly constant along the series at .9 cm. The combined length of the twenty ossicles amounts to 4.0 cm., giving an average height of .2 cm. per ossicle. The three large radials have a mean breadth of 1.1 cm., indicating a radial ring of diameter 1.9 cm., a trifle larger than that of Specimen B.

Specimen D. From the Wright collection. (Pl. 13).
This is little more than a mass of brachial and pinnular ossicles. The central succession may be IIBr2 to IIBr14 with outer pinnulation at IIBr2 and inner at IIBr4. Pronounced disarticulation of the succession is noted at IIBr7 and 8. As IIBr8 is the extreme ossicle preserved undisturbed in the specimen described by Brighton[4] or in any of these Yorkshire specimens, this ossicle might be taken as marking the point at which the secundibrachs become free from the calyx.

The individual represented is a very small one, its ossicles being rather less in size than those of Specimen A.


These specimens serve chiefly to confirm the views of Bather[5] and Springer[6] that the isolated plates found in the English chalk belong to the genus Uintacrinus found in the Uinta Mountains and in Westphalia. All specimens adhere to Bather’s rule of inner pinnulation at IIBr4, 7, 10 and outer at IIBr2, 5, 8. The figures of U. socialis, the American, and of U. westfalicus, the German species, indicate a difference in form that may best be conceived as due to the average width/height ratio of ossicles being less in the former. Consequently in the German form the plane of maximum diameter of the spheroidal cup passes through the primibrachs, whereas in the American form the cup continues to increase in diameter from the base to the level of the fourth secundibrachs. The impression of the Yorkshire specimens gained from a comparison of individual ossicles in figured specimens is one of closer resemblance to the German form than to the American. This impression has been confirmed by a comparison with actual specimens from Germany and America in the collections of the British Museum of Natural History. A further similarity then noted between the English and the German specimens is a tendency for the [faces] of ossicles to be rounded so that the structure of the cup is boldly defined, whereas in the American form the ossicles are flattened. It should be realised that this may be an unfair comparison since the German and English specimens have the advantage of preservation in sandy limestone and chalk respectively, whilst the American specimens examined are compressed in marly shale. Even admitting a close resemblance in form between the German and the English specimens there remains a discrepancy in size. The diameter of the radial ring of the type specimen of U. westfalicus is 2.4 cm.: none of the Yorkshire specimens exceed 2 cm. Hence, since the relative bulks are proportional to the cubes of the linear dimensions, the volume of the German form is of the order of twice that of the English form.


A feature brought out by this suite of specimens is the marked increase in boldness and angularity of ossicle-form with increase in size of specimen. This is well indicated by comparison of the photographs of Specimen A (Plate 10) and of Specimen B (Plates 11 and 12), and is taken as indicating the difference between young and mature individuals.

As mentioned in the description of Specimen D, there is some indication that brachials become free from the calyx at the level of the secundibrachs IIBr7 and 8.


The writer wishes to express thanks for assistance in the compilation of this paper to Dr. Alan Wood; the British Museum of Natural History for permission to examine German and American specimens of Uintacrinus; to the Museum of H.M. Geological Survey for the re-issue of Specimen A; to C. W. and E. V. Wright for the loan of Specimens C and D; and to E. V. Wright for preparing photographs of all four specimens.
















[1] Rowe, Proc. Geol. Assn., vol. xvi., 1900.

[2] Brighton, The Naturalist, Aug., 1936.

[3] Op. cit. [No. B 856].

[4] The Naturalist, Aug., 1936.

[5] Proc. Zool. Soc., London, for 1895, pp. 974-1004 (1896).

[6] Mem. Mus. Comp Zool. Havard, xxv., 1901.