the articulation (Pl. XIX. fig. 2). This cavity has two perforations. There is one long narrow superior perforation, which looks upward and extends for more than 4 inches in front of the articulation; it is margined externally by the surangular bone, internally, presumably, by the splenial. The internal lateral perforation is much smaller; its place is from 7 to 8 inches in front of the hindmost extremity of the jaw, and half an inch from its inferior border. Its lower border is made by the splenial bone (fig. 2 a), and its upper border probably by the surangular (fig. 2d), unless a small coronoid were present. The specimen does not show whether the perforations communicated or were separate. The internal cavity, like the jaw itself, is somewhat compressed from side to side behind on its inferior border, and widens a little anteriorly; it widens more from below upward. It is straight and in the same plane.

All the bones unite by sagittate sutures, and scarcely show any indications of squamous overlap. They are all more or less seen on the external aspect of the jaw (fig. 1), except the splenial bone; while every bone is seen on the internal aspect (fig. 2), where all the bones are free from sculpture. The internal aspect is largely occupied by the splenial element (fig. 2 a), which is fractured at its anterior extremity, and along all its upper border behind the lateral perforation. As preserved, it is 11 inches long, and was probably some inches longer. It terminates behind by a suture inclined slightly backward, but nearly vertical where it joins the articular bone (fig. 2 e); and it rests upon the angular bone (fig. 2 c) below, which extends along this aspect of the jaw for 74 inches. This suture with the angular bone has the outline of a low hill, of which the summit is at 3 inches from the hinder extremity, and the height about 1 inch. Hence the splenial bone descends in position as it passes forward, and then for 1 inch it crosses obliquely on the underside of the jaw, and so appears on its exterior aspect for 4 inches, extending forward as a very narrow strip, not a quarter of an inch deep (fig. 1a), which has the angular bone above it for 2 inches behind, and the dentary bone above it in front. It is strongly marked on the flattened underside of the jaw with a radiate ornament reaching through half a circle. The ornament extends from a centre on the inner margin of the bone, half an inch below an oblong vascular perforation on the inner aspect; around the centre are close-set pits; but further away these are elongated into grooves. Every pit and groove has a perforation or channel for one large blood-vessel.

Of the dentary bone only a small posterior part is preserved (fig. 1b). It extends backward on the upper surface of the jaw to within 2 inches of the articulation, and 4 inches of the extremity of the heel, terminating in a point. It rapidly widens and deepens. The surangular bone, over which it extends by squamous overlap, is internal to it on the superior aspect. Externally it descends down the side of the jaw by a long oblique suture, resting at first on the surangular bone for 14 inch, then on the angular bone for 53 inches, and finally upon the splenial bone. The dentary differs from the other external bones in being smooth and free from ornament, except faint longitudinal

striations. It is separated from the angular by a deep depression, looking as though due to its extension behind the angular, but probably resulting from the elevation of the ornament on the angular bone. The dentary bone makes an angular bend, so as to form a superior surface for the teeth, which appear to look upward and outward. Where the bone ends behind, the jaw extends for 24 inches below it, and inch above it, being 2 inches deep.

The angular bone (fig. 1 c) is the most striking part of the specimen. It forms the lower portion of the jaw on both aspects, and is an elongated bone tapering towards both ends on both sides. Externally it is 10 inches long, is received between the splenial and dentary bones in front, and posteriorly becomes depressed and reduced in depth from 13 inch at 5 inches from the end of the bone, to less than half an inch under the articulation. Its basal border is straight to within the posterior two inches, when it curves gently upwards, terminating half an inch short of the surangular bone, which extends along its superior 54 inches behind the point where the dentary bone terminates. This bone is marked by a semicircle of radiated sculpture, the centre of which is rather behind the middle of the bone on its basal border. As on the splenial bone, the ornament consists of an irregular honeycomb of pits near the centre, these becoming elongated laterally into grooves which run towards the extremities of the bone, harmonizing with the sculpture on the splenial and surangular elements. The grooves as they proceed become subdivided by ridges, of which five may be counted above the suture with the splenial bone at 8 inches from the end of the bone. The pits and grooves are full of perforations for blood-vessels, which take the same directions as the grooves. A broader groove, also vascular, shaped like the tail of a cursive y reversed, ascends to join the V-shaped groove on the surangular bone, which extends below the articulation of the jaw. These grooves only differ from the others in being broader. Altogether there are about 60 pits or grooves on the angular bone, mostly averaging inch in diameter, though some are punctures inch in size; while the broad posterior groove is half an inch in diameter, and the long anterior groove is 6 inches in length.

On the interior aspect of the jaw the angular bone occupies a smaller area (fig. 2, c). It reaches as far back, but not so far forward, as in front, being only about 74 inches long. Its greatest depth is 1 inch at 3 inches from its posterior end. The hinder part of the bone is concave from above downward, and has two conspicuous descending foramina under the part where it is deepest.

The surangular element (figs. 1, 2, 3, d) has hitherto been named the articular; but it extends in front of the articular bone so as to hide the whole of it except the surface seen in the articulation. The branch of the surangular which extends between the angular and dentary bones is about 5 inches long; but the part which, extending interior to the alveolar margin of the dentary bone, is imperfect anteriorly, is 84 inches long from the heel of the bone. Superiorly the bone bends over towards the inner side, so as to form a sort of back

ward prolongation of the alveolar table, nearly an inch wide. From this a sharp slightly elevated coronoid ridge [imperfectly preserved] arises, which extends forward in the median line, originating at the outer and anterior border of the articulation. Another ridge at right angles to this, and somewhat thicker, is directed outward, so that a concavity extends along the bone between them. This ridge extends backward for 3 inches, inclined very slightly downward, and then curves in a semicircle upward, to terminate just behind the articulation. Below this ridge, under the articulation, is a shallow groove less than inch wide, and below this an elevated-shaped rudely sculptured mass of ornament, 14 inch long and inch deep. Below this is the broad v-shaped groove, with a few tear-like ornaments. The hinder arm of the V extends upward behind the articulation; the front arm extends upward and forward; both arms are connected by the narrow curved groove below the articulation.

Behind the V-shaped groove is a triangular piece of vascular honeycomb-like ornament, 1 inch deep and 1 inch long at its base, where it is underlapped by the angular bone. It extends the jaw externally behind the articulation. Nothing is behind the straight inclined posterior line of this sculpture except the heel of the bone-a subquadrate process half an inch deep, developed backward and inward, so as with the angular bone below to nearly enclose the hindmost termination of the articular bone, which is greatly attenuated. The surangular bone is reflected behind the articular element, so that superiorly it almost meets the splenial element. Posteriorly, below the articulation, the bone is deeply impressed on the irregular smooth hinder surface.

The articular bone (figs. 1, 2, 3, e) forms a narrow strip on the inner side of the jaw, oblique and curved backward, extending from the articulation to below the heel of the surangular bone. The articular surface is subrhomboid, extending further backward and outward on the external margin, and further forward on the inner margin, which slightly overhangs the bones beneath. It measures inch from front to back, and 14 from within outward. Its greatest oblique measurement is less than 2 inches. The hinder margin (formed by the surangular bone) rises above the anterior margin. From back to front the area is semicylindrically concave, and marked with two broad slightly elevated ridges with a longitudinal groove between them, while a second incomplete sulcus forms the internal margin to the articulation.

Though the bones now described have a reptilian aspect, and somewhat of a reptilian arrangement, they do not go far towards suggesting the affinities of Labyrinthodon. There seems no reason to doubt that the central hollow space in the jaw received the primitive cartilage round which the bones were ossified; and the persistence of this character is rather a link with the lower than with the higher Vertebrata. The jaw differs from the Batrachian mandible in possessing well-developed angular and surangular elements, by which this cartilage and its articular ossification are enclosed. But some reptiles, such as Crocodiles and the marine

Chelonia, present many analogies in the perforations, in the structure of the jaw, and in the sculpture of the bones. But in the absence of more important parts of the skeleton, no conclusions can be drawn from these resemblances.

The species indicated by this specimen is almost identical in size with the fragment attributed by Mr. Miall to Labyrinthodon pachygnathus, and, so far as I can judge from figures, resembles that fossil closely both in form and ornamentation. But the depth and outline of the postarticular part of the jaw, and the differences of sculpture in the lateral subarticular ornament, supply characters for distinetion which, if the Warwickshire specimens are accurately figured, must separate the Dorsetshire fossil as a distinct species: this I propose to name Labyrinthodon Lavisi, in honour of its discoverer.

Associated Fragments. Within a yard or two of the spot where the jaw was found, Mr. Lavis picked up several other Labyrinthodont fragments, which he supposes, with good reason, to have been portions of the same skeleton. These comprise two small pieces of bones from the upper part of the skull, which are too imperfect to be determined with certainty at present, though one forms a portion probably of the orbit of the eye, and the other shows a portion of a narrow channel of the kind which has been called mucous groove: its radiated sculpture is finer than on the other specimens; and it may belong to a young animal or a small species. Another compressed curved bone about 2 inches long, inch deep at one end, narrowing along the curve, and less than inch thick, I am disposed to regard (if Labyrinthodont at all) as possibly a vomer. The concave border of the specimen appears to have been palatal. Along it, and on part of the adjacent side of the bone, extend three or four illpreserved rows of small conical teeth, which vary in size. These present a suggestive resemblance to the rows of teeth on the specimen figured by Prof. Huxley, and named Hyperodapedon, especially as some of them are similarly worn down; and it is possible that this fragment may pertain to that genus.

Two other specimens are portions of thoracic plates. A narrow fragment, 2 inches long, probably belongs to the median thoracic plate; while the principal fragment, 3 inches long and 13 inch wide, may be the right thoracic plate. It is thin, and marked by the usual radiated sculpture, but has the broad external border compressed and smooth.

Other smaller but imperfect plates were found, which are marked with shallow pits which do not become elongated into grooves. Another portion of bone may be a segment from the upper part of a strong rib.

A chevron bone (fig. 4) shows the articular surfaces on one side, which prove it to have been articulated between two vertebræ, as in most of the Reptilia and Palæosauria.

Portions of dense cylindrical or more compressed bones, having the appearance of weathered teeth, were found; but the transverse sections which Mr. Cuttell has endeavoured to prepare are too thick and opaque to demonstrate their real nature.

EXPLANATION OF PLATE XIX.

Fig. 1. External view of posterior part of right ramus of lower jaw.

2. Internal aspect of the same specimen.

3. Articular region, seen from above.

4. Chevron bone.

a, splenial bone; b, dentary bone; c, angular bone; d, suringular bone; e, articular bone.

DISCUSSION.

Mr. USSHER remarked that the Trias of South Devon was too variable in character to furnish reliable evidence as to the persistence of individual beds as lithological or paleontological zones. The conglomerate bed of Otterton Point, which crops out below High-Peake Hill, is cut out at Ladram Bay by a fault, but reappears towards Otterton Point for a distance of a mile and a half. It varies very much in character, and exhibits false bedding in parts. Organic remains have been found in the Trias at Ruishton, in a marly gritty conglomerate, which contains Labyrinthodon, Estheria, &c.—also near Stoke St. Mary's, where Estheria minuta occurs,-in the Vale of Taunton, in sandstone not contemporaneous with that on the coast, and at North Curry, where Estheria and plant-remains are found in arenaceous beds under marl.

Mr. WHITAKER stated that while Mr. Lavis's Labyrinthodon was obtained from near the top of the sandstone, his Hyperodapedon came from near its base.

Prof. RAMSAY remarked that all these bones were from the Keuper, and not from the Bunter.

The PRESIDENT (Prof. Duncan) said that Professor Seeley had very properly treated this bone from his own point of view; but he would no doubt admit that there were others from which it might be looked at. It seemed to him that if this were the lower jaw of Labyrinthodon, it was very distinct from any other specimen. He noticed that from Mr. Miall's description it would seem that he had got upon the trace of the surangular bone in Diadetognathus, as in one of his specimens he describes a ridge which may be the indication of a bone wanting in the Warwickshire specimen but present in this one. He thought that some fish exhibited a somewhat similar construction, but that the lower jaw alone could never be sufficient for the purpose of classification; and here the other and more essential parts of the skull were wanting. The Labyrinthodonts seemed to him to be unquestionably an order of Amphibia.

Mr. LAVIS, in reply, said that his estimate of the upthrow was made from the lithological characters of the beds. The zone indicated by him was not conspicuous by its lithological characters. It contained small grains of quartzite and pockets of marl.

Prof. SEELEY, after thanking the President for his remarks, stated Q. J. G. S. No. 127.

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