gularly fluted; a smooth boundary divides it from the crown, which is traversed by finer grooves converging to the apex; the transverse section of the crown is nearly circular, not compressed as in Ich. platyodon; it tapers gradually to the apex, which is nearer the posterior line than the central axis of the tooth.

The vertebræ are thicker in their antero-posterior diameter than in the Ich. platyodon: I count 45 between the occiput and pelvis, and 120 in the skeleton above-cited; but the tail is slightly imperfect. The scapula of the Ich. lonchiodon is more equably and deeply concave at the posterior margin, and its humeral extremity is relatively broader than in the Ich. platyodon. The bones of the extremities are thicker but shorter: the radius is emarginate anteriorly: there are three phalanges, of which the ossicles resemble in form those of the Ich. platyodon : but the whole paddle is relatively less. This difference is still more marked in the hind-paddle, which in the Ich. platyodon is, on the contrary, very nearly equal in size with the fore-paddle. Locality. The lias of Lyme Regis, where the skeleton abovenoticed was discovered by Miss Anning.

Ichthyosaurus tenuirostris*, Conybeare.

grandipes, Sharpe.

chirostrongulostinus, Hawkins.

The form of tooth figured by Mr. Conybeare as characteristic of the Ich. tenuirostris is one which it is very difficult to distinguish from that which is presented by the teeth of a species next to be described, and which in the form of its head is intermediate to the species called Ich. intermedius and Ich. tenuirostris. This species may, however, be recognised by other characters afforded by the humerus, the radius and tibia, and by the size and form of the paddle-bones, which have suggested the synonyms to their respective authors cited at the head of the present chapter.

But the most striking peculiarity of the Ichthyosaurus tenuirostris is that which Mr. Conybeare has happily chosen for its specific denomination, viz. the great length and slenderness of the jaw-bones, which are analogous in this respect to those of the Gharrial, and which, in combination with the large orbits and flattened cranium, give to its entire skull a close resemblance to that of a gigantic Scolopax, with a bill armed with teeth.

The length of the snout is chiefly due to the prolongation of * The characters derived from the relative length of the head, trunk, and tail, and of the fore and hind paddle, quoted from Cuvier, and assigned to the present species by H. V. Meyer, in his work entitled " Palæologica," p. 214, are those of the Ich. intermedius, to which species the small specimen figured by Home, in the Philosophical Transactions for 1819, and now in the Museum of the Royal College of Surgeons in London, belongs, and not, as Cuvier supposed, to the Ich. tenuirostris.

the intermaxillaries, and their analogues the dentary pieces of the lower jaw. These latter pieces have a longitudinal groove on their external surface near the alveolar ridge. The surangular disappears beneath the dentary about half an inch anterior to the nostril; the angular continues longer visible on the outside of the jaw.

The teeth are more slender in proportion to their length than in any of the previously described species: I count from 65 to 70 on each side of the upper jaw; of these the posterior third, or about 25, are implanted in the slender maxillary bones. In the lower jaw there are about 60 teeth on each side. They are directed more obliquely backwards than in the species previously described.

The parietals are divided by a persistent sagittal suture, and the foramen is principally situated in this suture, the anterior part only encroaching between the frontals. Each of the posterior parietal bifurcations runs parallel with, and is applied to the outside of the supraoccipital bone. The median frontals are also separated by suture; they are relatively larger than in communis, but do not reach the margin of the orbit. The anterior frontals lie on the outside of the median frontals; the posterior frontals on the outside of the parietals. Cuvier states that the post-frontals form the whole of the posterior boundary of the orbit. In the Ich. tenuirostris this boundary is slender, and presents a fine and deep smooth groove next the orbit.

I have already alluded to the large size of the orbits: they are not less characterized by the slenderness of their inferior and posterior parietes; the diameter of the orbit equals that of the posterior or occipital region of the cranium.

The malar bone is singularly long and slender, and brings to mind its characteristic condition in Birds: its posterior extremity is joined with a slender curved descending process of the zygomatic bone. The rest of the zygomatic element is much more robust, and passes obliquely backwards to join the articular extremity of the tympanic bone, and to circumscribe the temporal fossa below. The temporal fossa is bounded by the posterior frontals, the parietal fork, and by a bone which Cuvier regards as peculiarly Ichthyosaurian, and which extends from the postfrontals to the end of the parietal fork. The nasal bones have the margin which forms the upper boundary of the nostrils, slightly convex, encroaching upon the nostril. The nostrils are narrow and elongated, but apparently larger in proportion than in the other Ichthyosauri, measuring two inches and a half long in a head two feet in length now in the British Museum, and figured by Mr. Hawkins in his 13th Plate. The rami of the lower jaw soon unite, and the symphysis extends through more than the anterior two-thirds of the jaw.

The vertebral column corresponds in its general slenderness with the characteristic form of the head. The number of constituent vertebræ appears to be at least as great as in any previously described species of Ichthyosaurus: they are more variable in the antero-posterior direction, and have a more rounded and less angular contour than in any other species: their anterior and posterior articular surfaces are simply concave. A greater proportion of the terminal caudal vertebræ present the laterally compressed form than in other Ichthyosauri, which would indicate that the tegumentary caudal fin was of greater relative extent. The atlas or odontoid epiphysis of the vertebra dentata separates more easily from the body of that vertebra than is usual in other species of Ichthyosauri; and there appear to be only two subvertebral bones, viz. that beneath the occipital condyle, which represents the atrophied body of the atlas; and the second, developed in the angle between the axis and odontoid epiphysis; the third, which is usually situated between the axis and third cervical vertebra, is wanting in the present species. This simplification of the apparatus for fixing the neck accords with the light and slender character of the head. The vertebræ gradually increase in thickness, or anteroposterior extent, as they approximate the caudal region, whence they gradually diminish in all their dimensions. But at the posterior part of the abdomen, and beginning of the tail, they are relatively thicker in the direction of the axis of the body than in the other species of Ichthyosaurus. I count fifty vertebræ between the atlas and the first caudal vertebra.

The costal tubercle in the caudal vertebræ is situated near the anterior part of the centrum. The ribs are long and slender, and appear, in the present species, gradually to increase in length to near the posterior end of the vertebral column, and then to shorten more abruptly than usual.

The extremities of the Ich. tenuirostris are characterized in the first place by a disparity in the size of the fore and hind pairs similar to that which obtains in the Ich. communis and Ich. intermedius, and the fore paddles are more particularly distinguished by their massive proportions, as compared with the vertebræ.

The clavicles are slender, slightly expanded at the middle, and contracted at the two extremities; their anterior margin is inflected about 1 inch from their sternal extremity. The scapulæ are relatively larger than in the preceding species, bent and expanded at their humeral extremity.

The coracoids have a broad neck, a slight inferior emargination, and a deep and narrow superior notch.

In a well-preserved specimen of Ich. tenuirostris in the Birmingham museum,

The length of the humerus of the same specimen
Its breadth at the distal end

The humerus is characterized by the superior length of its shaft, and the sudden hammer-like expansion of its distal articular extremity, which, however, presents the usual flattened shape. The anterior or sternal surface of the humerus is produced into a strong angular process; its dorsal surface is nearly flat. The radial condyle is most produced, and the breadth of the radius equals nearly the transverse diameter of two of the bodies of the parallel vertebræ of the spinal column. The ulna, and the rest of the bones of the extremity, bear the same large proportional size. In the Ich. platyodon the breadth of the radius hardly equals the transverse diameter of a single parallel vertebra. In the Ich. communis and Ich. intermedius the breadth of the radius is less by one third than the transverse diameter of a vertebra from the corresponding part of the body. There is a small notch between the radius and ulna, at their proximal end, in the Ich. tenuirostris.

It is the large size of the two antibrachial bones, and especially the radius, that renders necessary the hammer-like extension of the anterior condyle of the humerus. In a specimen of Ich. tenuirostris from the Grafton Quarry lias near Warwick, at present in the museum of the Philosophical Institution of Birmingham, the radius and ulna are anchylosed together, and to the humerus. The specimen described by Prof. Jäger seems to present the same condition. The radius is distinguished, like that of the Ich. platyodon, by an emargination at the middle of its anterior edge.

The manus commences by three transversely oval carpal bones, and includes only four digital series of ossicles, which present a more rounded figure than in the previously described species, but resemble most in this respect the paddle-bones of the Ich. platyodon. The radial bone of the first or carpal series is notched anteriorly like the radius itself, but this character is not marked in the next bone below, as in the Ich. platyodon: the radial finger is not bifurcated.

In the hinder extremity of the Ich. tenuirostris the femur, like the humerus, has a longer shaft than usual, and also a greater transverse extension of its inferior condyles. The tibia, like the radius, is notched at its anterior edge, but the emargination is relatively wider and shallower, and notched also in a slight degree in the corresponding ossicle of the tarsal series.

The ossicle which is wedged into the interspace between the tibia and fibula is relatively smaller than the corresponding bone in the other Ichthyosauri; it seems, therefore, rather to form a

part of the cnemial than of the tarsal series; this latter row of three bones being completed by the intercalation, in its middle, of an ossicle which forms part of the third or metatarsal row in the intermedius and communis. The character above noticed in the tenuirostris may be observed, in a slighter degree, in the Ich. platyodon.

Size. In the museum of the Bristol Institution there is a magnificent though not complete skeleton of the Ich. tenuirostris, which measures thirteen feet in length. In Mr. Johnson's private collection, in the same city, there is a lower jaw of the Ich. tenuirostris from Lyme Regis, which measures two feet six inches in length: the exserted crown of one of the largest teeth in this specimen measures one inch and a half in length, and four lines in diameter across the base.

Localities.-The skeleton in the Bristol Museum is from the lias at Lyme Regis, where the species appears to be, however, less common than the Ich. communis and platyodon. The incomplete specimen from the lias of Stratford-on-Avon, in the museum of the Geological Society of London, and described by Mr. Sharpe under the name of Ichthyosaurus grandipes, belongs to the present species. Lord Cole possesses some characteristic fragments from the lias in the neighbourhood of Bristol. Evidences of the Ich. tenuirostris have been procured at Street and Walton, and at Barrow-on-Soar, in Leicestershire*.

This species undoubtedly exists in the lias formations of Boll and Amburg, in Wirtemberg†, and in the Jura limestone near Solothurn.

Ichthyosaurus acutirostris.

Under this name is indicated a species of Ichthyosaurus, which appears to be more common in the lias formations of the neighbourhood of Whitby than in those of Dorsetshire, although specimens also occur in the lias quarries of Street and Walton.

The teeth of the Ich. acutirostris, when they occur separately and singly, are hardly distinguishable from those of the

* Professor Sedgwick has an incomplete skeleton of the Ich. tenuirostris from this locality, in which the tail presents the abrupt and characteristic bend so common in the present genus; three of the ribs also of this interesting specimen have been fractured during the lifetime of the animal, and the fractured ends are rounded and expanded, and it is evident, that a false joint has been formed; the unintermitting respiratory movements having prevented a complete osseous reunion.

The skeleton of the Ich. tenuirostris in the Gymnasium of Wirtemberg is in some respects more complete than are any of those yet preserved in the museums of this country, not excepting the beautiful specimen in the museum of the Philosophical Institution of Birmingham. It is well described and figured by Professor Jäger, in his treatise "De Ichthyosauri Fossilis Speciminibus," fol. 1824, and has enabled me to ascertain the number of ribs which surround the thoracic-abdominal cavity, and at the same time test the constancy of the character derived from the form of the humerus and the emargination of the anterior edge of the radius and tibia.