imbedded in a slab of Tilgate grit, that is placed in the middle of the lowest compartment of this Case.

(nat. size.)

a. a. The spinous processes, from 13 to 15 inches in height.

b. b. Three displaced chevron bones, or hamapophyses, imbedded in the stone near their original position between the bodies of the vertebræ.

c. Anterior articular face of a vertebra.

The characters of the anterior caudal of a young Iguanodon are beautifully displayed in this invaluable specimen. The bodies of the vertebræ lie in natural juxta-position, the anterior oblique processes embracing the posterior; the spinous processes are entire and in their normal situation, and the transverse but little mutilated. Three displaced chevron-bones are imbedded near the corresponding articular surfaces of the bodies of the vertebræ, the proximal ends of two of them being almost in contact with the intervertebral spaces to which they belonged. The original position of the respective parts will be understood by reference to Lign. 35, p. 164, figs. 3, and 3 a, which is intended to illustrate the normal characters of the caudal vertebræ of the Iguanodon, and the

T

relative proportions of the apophyses; the figure is the size of the original.

Fig. 4 of the same lignograph is a lateral view of a caudal vertebra, remarkable for the deep cavity left between the centrum and the base of the neurapophysis, (o) by the removal of the pleural element or transverse process, which had dropped out before the bone was imbedded in the sandstone.

In the caudal vertebræ the centrum is more cuneiform than in the dorsals, the sides are smooth and almost flat vertically, and but slightly depressed in their antero-posterior diameter; at their inferior convergence, instead of uniting in a rounded ridge as in the dorsals, they are separated by a deep longitudinal furrow, bounded anteriorly and posteriorly by the oblique extremity of the centrum, which is truncated at both ends to articulate with the inferior spinous process or chevronbone (see fig. 3, Lign. 35). The articular faces of the bodies correspond with those of the posterior dorsals; the anterior surface is almost flat, the posterior slightly concave; the neural arch no longer presents the peculiar characters observable in the dorsal and lumbar vertebræ; it is attached by a wide base to the body, and the two laminæ in some instances extend transversely over the latter so as to complete the spinal canal, as in many of the dorsal vertebræ. The anterior zygapophyses (which are shown in Lign. 57) have their elliptical articular surfaces almost vertical, and closely embrace the corresponding posterior processes; the latter spring off from the base of the neural spine, and project over the centrum. The neural spine, or spinous process, is very long; it rises by an anterior basal ridge from the neural arch as in the dorsals, but is greatly contracted at its commencement, and increasing in breadth as it ascends, terminates in a thick truncated summit. The longest spine in the specimen before us is nearly 16 inches in height, and 2 inches in antero-posterior diameter at the summit; the spine is thin in a transverse direction, the truncated summit is but inch thick. The transverse processes are relatively short and strong. The height from the base of the centrum to the top of the spinous process is 22 inches, and as the chevron-bone, when perfect, would be nearly five inches in length, the vertical expansion of the tail in the young Igua

nodon to which these vertebræ belonged, must have been at least twenty-seven inches.

CHEVRON-BONE, or hamapophyses.-Wall-case C, left-hand shelf, lowest compartment.—The form of this element of the caudal region is well shown in this large and perfect specimen, which is figured in my "Fossils of Tilgate Forest," pl. xii. It is eleven inches in length, and 2 inches in antero-posterior diameter. The two laminae of which this bone essentially consists, are in the Iguanodon blended at the proximal end into an expanded cuneiform head, which fits into the corresponding intervertebral space left by the truncated angles of two contiguous vertebræ; and the distal portion constitutes a strong solid spine, a wide interspace, forming the canal for the passage of the large blood-vessels of the tail, being left at the upper part (as is shown in Lign. 35, fig. 2, 3, and 3 a, f, p. 164); this channel is three inches long in the specimen. before us. The blending of the proximal articular ends of the hæmapophyses into a single head, is constant throughout the caudal region of the Iguanodon, so far as my knowledge extends; among the hundreds of caudal vertebræ which I have examined, the unity of the hæmapophysial surface is distinctly impressed.'

OTHER VERTEBRA, in Wall-case C.-It would extend this article to an undue length were I to dwell on the anatomical characters of the other vertebræ in this Case, some of which, Dr. Melville and myself believe to be referable to the Iguanodon, while Professor Owen refers them to other genera. On many of these points the evidence appears to me to be insufficient to warrant a positive decision; and it will be most conducive to the successful elucidation of the subject by future inquirers, if, in this place, I subjoin a list of the specimens, with Professor Owen's interpretation of them.

1 The figure of a caudal vertebra with two distinct hæmapophysial surfaces, in Professor Owen's Monograph on "Cretaceous Fossil Reptiles," Pl. XXXVII. is certainly not a representation of a normal character: neither is the circular face of the centrum of the dorsal vertebra in Pl. XXXVI.; nor the posterior zygapophysis in Pl. XXXV. In fact, all these parts of the skeleton in the Maidstone specimen are so distorted, that it is impossible an artist can give the true characters of the original bones: especially when seen through the glass case that covers them.

Vertebra marked 12; body with the bases of the neural arch; figured in my "Fossils of Tilgate Forest," Pl. IX. fig. 11.

138 ;

2138

body of a dorsal vertebra.

These are assigned to the crocodilian reptile to which the slender, flat, acuminated teeth belong; under the name of Suchosaurus cultridens. A Caudal Vertebra-split vertically, the body having a central cavity which is filled with white calcareous spar, 2294) 2295 294 295 Referred to the Poikilopleuron; a crocodilian reptile found at Caen. Neural arch of an anterior dorsal vertebra 141: figured in "Fossils of Tilgate Forest," Pl. XII. fig. 1, is also provisionally referred to the same genus.

116

Two convexo-concave cervical vertebræ ; referred to Strepto spondylus major in "Brit. Assoc. Rep.," and now labelled S. recentior, in all probability belong to the Iguanodon.

Posterior caudal vertebræ 2112, 2142, 2153; referred to Cetiosaurus brevis.

Large posterior dorsal 183

2133

eight inches in diameter 15; these are also

referred to Cetiosaurus brevis.

Four perfect anterior caudals. These are also assigned to Cetiosaurus brevis; described provisionally by Dr. Melville as C. Conybeari, and since referred by me to the genus Pelorosaurus, to be described hereafter.

Two elongated subangular bodies of posterior caudals, figured in "Fossils of Tilgate Forest," Pl. IX. fig. 8, and Pl. X. fig. 1; assigned to Cetiosaurus brevis: referred to Iguanodon by Dr. Melville. The last reference, which appears to me the most probable, must, however, be regarded as only conditional.

Dorsal vertebra 10; assigned to Cetiosaurus brachyurus.

Caudal vertebra; to the same, referred by Dr. Melville to Iguanodon.

Dorsal vertebra 160 and 556

2180 255; referred to Iguanodon. Caudal vertebra 130 referred to the Iguanodon. Sacral vertebra 127 2127; to the same.

2130 ;

All the specimens above enumerated are described in "Reports on Brit. Foss.," with that minuteness of detail and consummate skill, which characterise the anatomical investigations of the Hunterian Professor.

The following extract from Professor Melville's commentary on the above generic and specific determinations will put the scientific inquirer in possession of the opinions of that eminent anatomist on the questionable references:-"I can perceive no difference between the posterior dorsal or lumbar vertebræ (No. 2,133, 2,115) assigned by Professor Owen

1 The numbers refer to those affixed to the specimens in the "Catalogue of the Mantellian Collection in the British Museum."

to the Cetiosaurus brevis, and that last described as corresponding in some respects to the fifth dorsal in the spinal column of the Crocodile, than a diminution in the relief of the buttress supporting the transverse process. In No. 2,115 the neural arch is broken away, and the tract of the centrum left uncovered behind to form the floor of the intervertebral foramen, is of greater extent than in No. 2,133, indicating a more posterior situation in the vertebral series. The approach to the quadrangular form of the body of this vertebra is no proof whatever of a specific and still less of a generic distinction; otherwise the first sacral vertebra, which is more decidedly quadrate, if found separate, would be equally entitled to a generic value; but its association, in the sacrum from Mr. Saull's collection, with other vertebral bodies of a very dissimilar character, and with the ilium of the Iguanodon, prevents our falling into an error of such magnitude. We may therefore reasonably conclude, that these vertebræ, to wit, Nos. 2,133, 2,115, belong to the Iguanodon, and that No. 2,115, in the form of the body, approached the first sacral, and was one of the proper lumbar series.

"The vertebra, No. 2,109, attributed in the above-mentioned report to the (so-called) second species of Cetiosaurus found in the Wealden formation (C. brachyurus), is also a posterior dorsal or lumbar vertebra of the Iguanodon; the neural arch is much mutilated. The only other element of the skeleton of that species is a caudal vertebra, No. 2,161, which also belongs to the Iguanodon; being in fact one of the most anterior of the caudal series, and contrary to the character of the genus to which it was referred, it presents one of the most interesting and instructive examples of the rough surface on the sides of the upper aspect of the centrum, left by the removal of the unanchylosed neural arch. The so-called Cetiosaurus brevis being thus founded only on two vertebræ which belong to the Iguanodon, must be expunged from the list of extinct reptiles.

"The angular posterior caudal vertebræ referred in the Report on British Reptiles, to the Cetiosaurus brevis, I am also inclined to assign to the Iguanodon for the following reasons:-1stly, a similar vertebra, as far as can be ascertained, exists in the Maidstone specimen, and in this case an admixture of bones of distinct animals can scarcely be suspected; 2dly, the numerical ratio of the vertebræ of this kind occurring in the Wealden, to those from the same deposits and localities belonging to other regions of the spinal column, all referable to the Iguanodon, excepting the few megalosaurian and crocodilian vertebræ, is such as long ago to have induced Dr. Mantell to regard them as characteristic of that saurian; and the occurrence of such vertebræ with those of the sacrum and other bones of the Iguanodon in Western Sussex, described by Cuvier, has already been commented on:1-3dly,

1 In reference to the somewhat angular caudals, alluded to in the text, I would remark that with the unquestionable sacral vertebræ of the Iguanodon found at Loxwood, and transmitted to Baron Cuvier by Sir Roderick Murchison, (ante, p. 269,) there were several that appeared to belong to the same individual, which possessed the angular form and sulcated base of the bones described in the text, as may be seen by