Head.[1]
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.[2]
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 a 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 conjecturally 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, vol. 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 anterior 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-
