OWEN.— CLASSIFICATION OF REPTILIA. 79 
Order I11.—Ichthyopterygia.—The bones of the head still include the supple- 
mentary “ post-orbitals” and “ supra-temporals,” but there are small temporal and 
other vacuities between the cranial bones: a “ foramen parietale,” a single convex 
oceipital condyle,* and one vomer which is edentulous. Two antorbital nostrils. 
Vertebral centra, ossified, biconcave. Pleurapophyses of the trunk long and bent 
the anterior ones with bifurcate heads. Teeth with converging folds of cement at 
their base ; implanted in a common alveolar groove, and confined to the maxillary, 
premaxillary, and premandibular bones. Premaxillaries much exceeding the 
maxillaries in size. Orbit very large: a circle of sclerotic plates. Limbs nata- 
tory; with more than five multi-articulate digits; no sacrum. With the retention 
of characters which indicate, as in the preceding orders, an affinity to the higher 
Ganoidea, the present exclusively marine Reptilia more directly exemplify the 
Ichthyic type in the proportions of the premaxillary and maxillary bones; in the 
shortness and great number of the biconcave vertebrze; in the length of the pleur- 
apophyses of the vertebrz near the head; in the large proportional size of the 
eyeball, and its well-ossified sclerotic coat, and especially in the structure of the 
‘pectoral and ventral fins. The skin isnaked. The order ranges from the lias to 
the chalk. 
Order 1V.—Sauropterygia.—No post-orbital and supra-temporal bone: large 
temporal and other vacuities between certain cranial bones ; a foramen parietale; 
two antorbital nostrils ; teeth simple, in distinct sockets of premaxillary, maxillary, 
and premandibular bones, rarely on the palatine or pterygoid bones; maxillaries 
larger than premaxillaries. Limbs natatory; not more than five digits. A 
sacrum of one or two vertebre for the attachment of the pelvic arch in some, 
numerous cervical vertebree in most. Pleurapophyses with simple heads; those 
of the trunk long and bent. Inthe Pliosaurus the neck vertebre are compara- 
tively few in number, short and flat. The sauropterygian type seems to have 
attained its maximum dimensions in this genus: the species of which are peculiar 
to the Oxfordian and Kimmeridgian divisions of the Upper Oolitic system. M. 
von Meyer regards the number of cervical vertebre and the length of neck as 
characters of prime importance in the classification of Reptilia, and founds thereon 
his Order called Macrotrachelen, in which he includes Simosaurus, Pistosaurus 
and Nothosaurus, with Plesiosaurus. No doubt the number of vertebree in the 
same skeleton bears a certain relation to ordinal groups; the Ophidia find a com- 
mon character therein; yet it is not their essential character; for the snake-like 
form, dependent on multiplied vertebra, characterizes equally certain Batrachians 
(Cecilia) and fishes (Murena). Certain regions of the vertebral column are the 
seats of great varieties in the same natural group of Reptilia. We have long- 
tailed and short-tailed lizards: but do not, therefore, separate those with numerous 
caudal vertebra, as “ Macrourau,” from those with few or none. The extinct 
Dolichosaurus of the Kentish chalk, with its procclian vertebre, cannot be ordin- 
ally separated, by reason of its more numerous cervical vertebre, from other 
shorter-necked proccelian lizards. As little can we separate the short-necked and, 
the big-headed amphiccelian Pliosaur from the Macrotrachelians of Von Meyer- 
* This character is retained throughout the rest of the class, save in Batrachia, and will 
not afterwards be expressed in their characters. 
+ These bones do not reappear in the subsequent orders. 
