Dermal Spines of Hylæosaurus. [Lign. 208], fig. 4.—With the dermal bones above described there are associated in the first discovered specimen of the Hylæosaurus, flat, thin, angular, osseous plates, from three to seventeen inches in length; one of which is figured [Lign. 208], fig. 4. The manner in which they are imbedded in the rocks, in connexion with other parts of the skeleton, is shown Wond. pl. iv. and Geol. S. E. pl. v. These very remarkable processes appeared to me to have formed part of a serrated fringe, which extended along the back of the reptile, analogous to that observable in certain living lizards (Wond. p. 436, [Lign. 108]); and were provisionally described as such in my first memoir on the Hylæosaurus. This conjecture has been substantiated by subsequent discoveries, and the true nature of the large, flat, angular spines, and the conical bones resembling the horn-cones of ruminants, which occur in the Wealden, is now established.[589]

[589] See Fossils, Brit. Mus. pp. 298, 320.

Horn of Iguanodon.—In this category may be placed the nasal tubercle or horn of a saurian, like that of the Iguana ([Lign. 208], fig. 2; Geol. S. E. pl. iii.), found with the remains of the Iguanodon, and probably belonging to that colossal reptile (Wond. p. 431; and Petrif. p. 298). It is four inches in length and 3.2 inch by 2.1 inch in diameter at the base, which is of an irregular elliptical form. Several smaller specimens have recently been discovered.

Examples of dermal scutes and spines, presenting modifications of form and structure distinct from those above described, have been brought to me from various localities of the Wealden; but, as in no instance a connexion with other parts of the skeleton could be traced, the particular reptiles to which they belonged cannot be ascertained.

We proceed to notice some of the principal genera of Fossil Reptiles, especially of those whose remains occur in the British strata; the arrangement of Professor Owen is adopted for the convenience of reference to the Brit. Assoc. Reports, 1839 and 1841, which should be consulted by the student who would acquire a knowledge of this department of Palæontology. The subject will be considered under the following heads; namely:—

I.[Enaliosaurians], or Marine Reptiles; Ichthyosaurus and Plesiosaurus.
II.[Crocodilians]; Crocodile, Teleosaur, &c.
III.[Deinosaurians]; comprising the Iguanodon, Megalosaurus, Hylæosaurus, Pelorosaurus, &c.
IV.[Lacertians]; including the Mosasaurus, Rhyncosaurus, &c.
V.[Pterosaurians]; the Pterodactyles, or flying Reptiles.
VI.[Chelonians]; or Tortoises and Turtles.
VII.[Ophidians]; or Serpents.
VIII.[Batrachians]; or the Frog tribe; comprising the Labyrinthodonts.

I. Enaliosaurians.—The extinct marine reptiles comprised in this order constitute two genera, which are characterized by essential modifications of osteological structure; they are named Ichthyosaurus (fish-lizard), and Plesiosaurus (akin to a lizard). The general appearance of these beings is so well known, from the splendid collection of their fossil remains in the British Museum, and the numerous specimens in provincial and private collections, and by various works, both scientific and popular, in which their structure and physiological relations are fully elucidated, that they must be familiar to every reader.[590]

[590] Bd. vols. i. and ii. contain an admirable exposition of their habits and organization; and Brit. Assoc. Reports, 1839, 1841, elaborate osteological investigations of both genera. A folio volume on these extinct Reptiles, with splendid lithographs, by Thomas Hawkins, Esq., cannot fail to delight the reader by its graphic descriptions and beautiful illustrations. See also the masterly paper on the Ichthyosaur and the Plesiosaur, by the Rev. W. D. Conybeare, in the Geological Transactions, 1st series, vol. v. p. 559, et seq.

ICHTHYOSAURUS. PLESIOSAURUS.