the fossil worm-like bodies, so abundant in the lithographic slate of Solenhofen, and described by Count Münster in the Petrefacten of Goldfuss, under the name of Lumbricaria, are either the petrified intestines of fishes, or the contents of their intestines, still retaining the form of the tortuous tube in which they were lodged. To these remarkable fossils he has given the name of Cololites. (Pl. 15', is copied from one of a series that are engraved in Goldfuss. Petrefacten, Pl. 66.) He has also found similar tortuous petrifactions within the abdominal cavity of fossil fishes, belonging to several species of the genus Thrissops and Leptolepis, occupying the ordinary position of the intestines between the ribs.* (See Agassiz Poissons Fossiles, liv. 2, Appendix, p. 15.)

It is probable that to many persons inexperienced in anatomy, any kind of information on a subject so remote, and apparently so inaccessible, as the intestinal structure of an extinct reptile or fossil fish, may at first appear devoid of the smallest possible importance; but it assumes a character of high value, in the investigation of the proofs of creative

* As these Cololites are most frequently found insulated in the lithographic limestone, M. Agassiz has ingeniously explained this fact by observing the process of decomposition of dead fishes in the lakes of Switzer. land. The dead fish floats on the surface with its belly upwards, until the abdomen is so distended with putrid gas, that it bursts: through the aperture thus formed the bowels come forth into the water, still adhering together in their natural state of convolution. This intestinal mass is soon torn from the body by the movement of the waves; the fish then sinks, and the bowels continue a long time floating on the water: if cast on shore, they remain many days upon the sand before they are completely decomposed. The small bowels only are thus detached from the body, the stomach and other viscera remain within it.

We owe this illustration of the nature of these fossil bodies, whose origin has hitherto been inexplicable, to the author of a most important work on fossil fishes, now under publication at Neuchatel. His qualifications for so great and difficult a task are abundantly guaranteed by the fact, that Cuvier, on seeing the progress he had made, at once placed at the disposal of Professor Agassiz the materials he had himself collected towards a similar work.

wisdom and design, that are unfolded by the researches of Geology; and supplies a new link to that important chain, which connects the lost races that formerly inhabited our planet, with a species that are actually living and moving around ourselves.* The systematic recurrence, in animals of such distant eras, of the same contrivances, similarly disposed to effect similar purposes, with analogous adaptations to peculiar conditions of existence, shows that they all originated in the same Intelligence.

When we see the body of an Ichthyosaurus, still containing the food it had eaten just before its death, and its ribs still surrounding the remains of fishes, that were swallowed ten thousand, or more than ten times ten thousand years ago, all these vast intervals seem annihilated, time altogether disappears, and we are almost brought into as immediate contact with events of immeasurably distant periods, as with the affairs of yesterday.

SECTION VI.

PLESIOSAURUS.†

WE come next to consider a genus of extinct animals, nearly allied in structure to the Ichthyosaurus, and co-extensive with it through the middle age of our terrestrial history. The discovery of this genus forms one of the most important additions that Geology has made to comparative

* Le temps qui répand de la dignité sur tout ce qui échappe à son pouvoir destructeur, fait voir ici un exemple singulier de son influence: ces substances si viles dans leur origine, étant rendues à la lumière après tant de siècles, deviennent d'une grande importance puis qu'elles servent à remplir un nouveau chapitre dans l'histoire naturelle du globe.-Bulletin Soc. Imp. de Moscow, No. VI. 1833, p. 23.

† See Pl. 16, 17, 18, 19.

VOL. K-14.

anatomy. It is of the Plesiosaurus, that Cuvier asserts the structure to have been the most heteroclite, and its characters altogether the most monstrous, that have been yet found amid the ruins of a former world. To the head of a Lizard, it united the teeth of a Crocodile; a neck of enormous length, resembling the body of a Serpent: a trunk and tail having the proportions of an ordinary quadruped, the ribs of a Chameleon, and the paddles of a Whale. Such are the strange combinations of form and structure in the Plesiosaurus-a genus, the remains of which, after interment for thousands of years amidst the wreck of millions of extinct inhabitants of the ancient earth, are at length recalled to light by the reseaches of the Geologist, and submitted to our examination, in nearly as perfect a state as the bones of species that are now existing upon the earth.

The Plesiosauri appear to have lived in shallow seas and estuaries, and to have breathed air like the Ichthyosauri, and our modern Cetacea. We are already acquainted with five or six species, some of which attained a prodigious size and length; but our present observations will be chiefly limited to that which is the best known, and perhaps the most remarkable of them all, viz. the P. Dolichodeirus.†

* Cet habitant de l'ancien monde est peut-être la plus hétéroclite et celui de tous qui paroît le plus mériter le nom de monstrc.-Oss. Foss. V. Pt. 2, p. 476.

The first specimens of this animal were discovered in the lias of Lyme Regis, about the year 1823, and formed the foundation of that admirable paper (Geol. Trans. Lond. vol. 5, Pt. 2.) in which Mr. Conybeare and M. De la Beche established and named this genus. Other examples have since been recognised in the same formations in different parts of England, Ireland, France, and Germany, and in formations of various ages, from the muschel kalk upwards to the chalk. The first specimen discovered in a state approaching to perfection, was that in the collection of the Duke of Buckingham, (figured in the Geol. Trans. Lond. N. S. Vol. 1, Pt. 2, Pl. 48.) Another specimen, nearly entire, in the collection of the British Museum, eleven feet in length, is figured in our second volume, Pl. 16;) and at Pl. 17, a still more perfect fossil skeleton, also in the British Museum, discovered by Mr. Hawkins, in the

Head.*

The head of the P. Dolichodeirus exhibits a combination of the characters of the Ichthyosaurus, the Crocodile, and the Lizard, but most nearly approaches to the latter. It agrees with the Ichthyosaurus in the smallness of its nostrils, and also in their position near the anterior angle of the eye; it resembles the Crocodile, in having the teeth lodged in distinct alveoli; but differs from both, in the form and shortness of its head, many characters of which approach closely to the Iguana.†

lias at Street, near Glastonbury. At Pl. 16 is also copied Mr. Conybeare's restoration of this animal, from dislocated fragments, before any entire skeletons were found. The near approach of this restoration to the character of the perfect skeletons, affords a striking example of the sure grounds on which comparative anatomy enables us to reconstruct the bodies of fossil animals, from .. careful combination of insulated parts. The soundness of the reasoning of Cuvier, on the fossil quadrupeds of Montmartre, was established by the subsequent discovery of skeletons, such as he had conjectu. rally restored from insulated bones. Mr. Conybeare's restoration of the Plesiosaurus Dolichodeirus, (Pl. 16,) was not less fully confirmed by the specimens above-mentioned,

* See Pl, 16, 17, 18.

+ Mr. Conybeare, in the Geol. Trans. second series, vcl. 1, part 1, Pl. 19, has published figures of the superior and lateral view of a nearly perfect head of this animal, Our figure, Pl. 18, Fig. 2, represents the head of the specimen in the British Museum, of which the entire figure, on a smaller scale, is given in Pl. 16. The head is in a supine position; the upper jaw is distorted, and shows several of the separate alveoli that contained the teeth, and also the posterior portion of the palate. The under jaw is but little disturbed.

A figure of another lower jaw is given at Pl. 18, Fig. 1, taken from a specimen also in the British Museum, found by Mr. Hawkins, at Street.

Pl. 19, Fig. 3, represents the extremity of the dental bone of another lower jaw, in the same collection, retaining several teeth in the anterior sockets, and also exhibiting a series of new teeth, rising within an inte rior range of small cavities. This arrangement for the formation of new teeth, in cells within the bony mass that contains the older teeth, from which they shoot irregularly forwards through the substance of the bone, forms an important point of resemblance whereby the Plesiosaurus as

Neck.

The most anomalous of all the characters of P. Dolichodeirus is the extraordinary extension of the neck, to a length almost equalling that of the body and tail together, and surpassing in the number of its vertebræ (about thirty-three) that of the most long-necked bird, the Swan: it thus deviates in the greatest degree from the almost universal law, which limits the cervical vertebræ of quadrupeds to a very small number. Even in the Camelopard, the Camel, and Lama, their number is uniformly seven. In the short neck of the Cetacea the type of this number is maintained. In Birds it varies from nine to twenty-three; and in living Reptiles from three to eight.* We shall presently find in

sumes, in the renovation of its teeth, the character of Lizards, combined with the position of the perfect teeth in distinct alveoli, after the manner of Crocodiles.

The number of teeth in the lower jaw was fifty-four, which, if met by a corresponding series in the upper jaw, must have made the total number to exceed one hundred. The anterior part of the extremity of the jaw enlarges itself like the bowl of a spoon, to allow space for the reception of the first six teeth on each side, which are the largest of all.

*To compensate for the weakness that would have attended this great elongation of the neck, the Plesiosaurus had an addition of a series of hatchetshaped processes, on each side of the lower part of the cervical vertebræ. (Pl. 17, and Pl. 19, 1, 2.) Rudiments and modifications of these processes exist in birds, and in long-necked quadrupeds. In the Crocodiles they assume a form, most nearly approaching that which they bear in the Plesio

saurus.

The bodies of the vertebræ also more nearly resemble those of certain fossil Crocodiles, than of Ichthyosauri or Lizards; they agree farther with the Crocodile, in having the annular part attached to the body by sutures; so that we have in the neek of the P. Dolichodeirus a principle of construction resembling that of the vertebræ of Crocodiles; combined with an elongation very much exceeding that of the longest neck in birds, and such as occurs in no other known animal of the extinct or living creations. The length of the neck in P. Dolichodeirus is nearly five times that of the head; that of the trunk four times the length of the head, and of the tail three times; the head itself being one-thirteenth part of the whole body. See Geol. Trans. Lond. Vol. 5, p. 559, and Vol. I. N. S. p. 103, et seq.