| OCR Text |
Show 978 MR. F. A. BATHER ON UINTACRINUS. [DeC. 17, Two slabs from the same locality, collected by Mr. H. T. Martin, have recently been purchased by the Trustees of the British Museum. Since they are the only specimens of the genus in England, and probably the only specimens of U. socialis as yet received in Europe \ the description of them that Dr. Henry Woodward has kindly permitted me to draw up may interest English naturalists. At the same time, the more careful investigation that these exceedingly beautiful specimens have rendered possible has enabled a few details to be more accurately filled in. The larger of the two slabs has an irregular area of about 2400 sq. cm., aud contains 23 cups, one of which shows the base very clearly ; the arms are also well shown. This slab represents the unweathered condition of the fossil; the matrix is a soft, calcareous yellow shale, in general aspect reminding one of the Solenhofen Lithographic Stone, but much softer and more friable. According to Prof. S. Calvin2, it is composed of microscopic organisms identical wdth those of true chalk. Where the crinoids are massed together, their calcareous remains form, as described by Prof. Williston, a dense plate. As a rule, however, the separate plates and ossicles of the crinoid are far too easily detached from the matrix. The calyces are flattened out, and the arm-ossicles also are much compressed, so that their examination is not easy. This slab, registered E 6527, is now exhibited in Gallery No. 8 of the Geological Department of the British Museum (Nat. Hist.). For convenience of reference the cups contained on it have been lettered a, b, c, &c. The smaller of the two slabs, with an area of 420 sq. cm., contains the remains of 7 cups, of which three show the basal circlet. This slab represents the weathered condition of the fossil, which fact, however, rather facilitates than hinders study. The shale is a pale bluish grey, and the pale yellow plates stand out clearly, both in colour and relief. This slab is registered E 6328, and the cups are lettered a, )}, y, &c. Both these slabs show a feature of fossilization hitherto unnoticed in Uintacrinus; iu fact, so far as I am aware, unknown among crinoids. That is, the preservation of a thin layer of carbonaceous material, which lines the interior of the calyx. Unfortunately, the traces of microscopic structure exhibited by this are of the most meagre description. 2. MORPHOLOGICAL DESCRIPTION OF UINTACRINUS SOCIALIS. The crinoid consists of a crown only. There is no trace of a stem, unless, indeed, the central apical plate be the diminished representative of the proximal columnal, for which view there is no evidence. 1 Geh. Professor Karl von Zittel informs me, in a letter dated January 18, that the Munich Museum has also acquired similar specimens. 2 " The Niobrara Chalk." Presidential Address, Proc. Amer. Assoc, xliii. pp. 197-217 (1894); and in a private letter to the author, January 1896. |
