Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/590

 2. Note on an Ichthyosaurus (I. enthekiodon) from Kimmeridge Bay, Dorset. By J. W. Hulke, Esq., F.R.S., F.G.S.

[Plate XVII.]

On the 22nd December, 1869, I brought under the notice of the Society two fragments of a long, slender snout with sauroid teeth of a peculiar form, obtained in Kimmeridge Bay by J. C. Hansel, Esq., F.G.S., which I was inclined to refer to the genus Ichthyosaurus ; but the evidence not being quite decisive I was obliged to leave the true position of the Saurian indicated by them to be determined at some future time, whenever new material for the purpose might accrue. Meanwhile I gave it the provisional name Enthekiodon, from the thick capsule of cementum surrounding the tooth-fang.

A very few days afterwards, while making a short visit with Mr. Mansel to Kimmeridge Bay, we discovered great part of the skeleton of an indubitable Ichthyosaurus, the snout and teeth of which agreed so closely with those of Enthekiodon as to leave no reasonable doubt of their identity, Mr. Mansel generously added it to the splendid series of Kimmeridge fossils already presented by him to the British Museum, and it has lately been placed in the Palaeontological Gallery.

The skeleton lies (as we found it on the reef) on its left side ; the head is bent upwards, the vertebral column makes a double curve, the greater part of the tail is missing, a large number of the ribs on the right side preserve their relations to the vertebral column and to one another nearly undisturbed ; beneath them is a black stain (cuttle-ink ?), in which are small scales ; below the early thoracic ribs lie the bones of the breast-girdle. The least mutilated fore- paddle was inadvertently taken from the situation where I saw it before the skeleton was removed by the quarrymen ; and it and the remaining hind paddle have been fixed in the slab below the skeleton.

The anatomical details of the skull are not decipherable ; but the orbit is large, and the eyeball has the usual bony ring.

The entire length of the head is 23-5 inches. The jaws are very long and slender. The teeth are smooth, slender, cylindrical, and pointed ; they are composed of an internal core of simple tubular dentine, the crown overlaid with enamel, and the root enveloped in a thick smooth sheath of vascular cementum, which gives it a bulbous figure. The basal end of the cylinder of dentine contracts slightly, and it is also slightly and irregularly indented, very faintly shadowing, as it were, the beautiful inflexions of the dentine and cementum of the same part in the tooth of I. communis. The apex of the pulp-cavity rises into the crown ; it is filled with a brittle cone of spar ; and the base of the cavity contains a small plug of osteodentin, the vascular canals of which inosculate through the open end of the cavity with those of the external sheath of cement, just as in I. communis.

In the spinal column 56 vertebra;, connected in an unbroken series, now occupy 8 feet ; but the hinder ones have slipped slightly