RHYNCHOSAURUS, Ow.
Sp. Rhynchosaurus articeps, fossils in which the above order, genus, and species of reptile have been based are from the new red sandstone (trigs) of Shropshire. They occur at the Grinsill quarries, near Shrewsbury, in a fine grained sandstone, and also in a coarse burr-sandstone ; in the latter the writer found imbedded some vertebrae, portions of the lower jaw, a nearly entire skull, fragments of the pelvis and of two femora : in the fine-grained sandstone, vertebra., ribs, and some bones of the scapular and pelvic arches are imbedded. The bones preseut a very brittle and compact texture ; the exposed surface is usually smooth, or very finely striated, and of a light blue colour. The sandstones containing these bones occasionally exhibit impressions of footsteps which resemble those figured in the Memoir by Murchison and Strickland (Geol. Trans., 2d series, vol. v., pL xxviii. fig. 1) ; but they differ in the more distinct marks of the claws, the less distinct impression of a web, the more diminutive size of the innermost toe, and an impression corresponding with the hinder part of the foot, which reminds one of a hind toe point ing backwards, and which, like the hind toe of some birds, only touched the ground with its point. The footprints are likewise more equal in size, and likewise in their intervals, than those figured in the above-cited Memoir : they measure from the extremity of the outermost or fifth toe to that of the innermost or first rudimental toe, about one inch and a half. They are the only footprints that have as yet been detected in the new red sandstone quarries at GrinsilL As the fossil bones have always been found nearly in the same bed as that impressed by the footsteps above described, they probably belong to the same animaL In the vertebrae both articular surfaces of the centrum are concave, and are deeper than in the biconcave vertebrae of the extinct Croco dilians ; the texture of the centrum is compact throughout The neural arch is anchylosed with the centrum, without trace of suture, as in most lizards ; it immediately expands and sends outwards from each angle of its base a broad tri angular process with a flat articular surface ; the two anterior surfaces look directly upwards, the posterior ones downwards ; the latter are continued backwards beyond the posterior ex tremity of the centrum ; the tubercle for the simple articula tion of the rib is situated immediately beneath the anterior oblique process. So far the vertebra of the Rhynchosaurus,
always excepting their biconcave structure, resemble the vertebra of most recent lizards. In the modification next to be noticed, they show one of the vertebral characters of the Dinosauria. A broad obtuse ridge rises from the upper convex surface of the posterior articular process and arches forwards along the neural arch above the anterior articular process, and gradually subsides anterior to its base : the upper part of this arched angular ridge forms, with that of the opposite side, a platform, from the middle line of which the spinous process is developed. Nothing of this kind is present in existing lizards ; the sides of the neural arch immediately converge from the articular processes to the base of the spine, without the inter vention of an angular ridge formed by the sides of a raised platform. The base of the spinous process is broadest behind, and commences there by two roots or ridges, one from the upper and back part of each posterior articular process. The anterior margin of the spinous process is thin and trenchant ; the height of the spine does not exceed the antero-posterior diameter of its base ; it is obliquely rounded off. The spinal canal sinks into the middle part of the centrum and rises to the base of the spine, so that its vertical diameter is twice as great at the middle as at the two extremities : this modification resembles in a certain degree that of the vertebra of the Palceosaurus from the Bristol conglomerate.