ON FOSSIL AND RECENT KEPTILIA. 159 



There is nothing in the known structure of the so-named Archegosaurus 

 or Mastodonsaurus that truly indicates a belonging to the Saurian or Croco- 

 dilian order of reptiles. The exterior ossifications of the skull and the 

 canine-shaped labyrinthic teeth are both examples of the Salamandroid 

 modification of the ganoid type of fishes. 



The small proportion of the fore-limb of the Mystriosaurus in nowise 

 illustrates this alleged saurian affinity, for, though it be as short as in Arche- 

 gosaurus, it is as perfectly constructed as in the Crocodile ; whereas the short 

 fore limb of Archegosaurus is constructed after the simple type of that of the 

 Proteus and Siren. But the futility of this argument of the sauroid affinities 

 is made manifest by the proportions of the hind limb of Archegosaurus; 

 it is as stunted as the fore limb : in the Labyrinthodonts it presented larger 

 proportions, which, however, may be illustrated as naturally by these pro- 

 portions in the limbs of certain Batrachia as by the proportions of the limbs 

 of Teleosaurus. 



Older III. ICHTHYOPTERYGIA. 



This name, from 'i\Qvs, a fish, and nrepvE,, a wing or fin, relates to the piscin 

 character of the numerous and many-jointed rays or digits in the fore and 

 hind paddles. The bones of the head still include the supplementary 'post- 

 orbital' and 'supratemporal ' bones, but there are small temporal and other 

 vacuities between the cranial bones, including a 'foramen parietale;' there is 

 a single, convex, occipital condyle* ; and one vomer, which is edentulous. 

 There are two antorbital nostrils. The vertebral centra are ossified and bi- 

 concave. The pleurapophyses of the trunk are long and bent ; the anterior 

 ones with bifurcate heads. The teeth have converging I olds of cement at 

 their base, are implanted in a common alveolar groove, and are confined to 

 the maxillary, premaxillary, and premandibular bones ; the premaxillaries 

 much exceeding the maxillaries in size. The orbits are very large ; the eyes 

 were defended by a broad circle of sclerotic plates. The limbs are natatory, 

 with more than five multiarticulate digits ; there is no sacrum. 



With the retention of characters which indicate, as in the preceding orders, 

 an affinity to the higher Pisces Ganoidei, the present exclusively marine Pep- 

 tilia more directly exemplify the Ichthyic type in the proportions of the pre- 

 maxillary and maxillary bones, in the shortness and great number of the bi- 

 concave vertebrae, in the length of the pleurapophyses of the vertebras near 

 the head, in the large proportional size of the eye-ball and its well-ossified 

 sclerotic coat, and especially in the structure of the pectoral and ventral fins. 



Order IV. Sauropterygia. 



The fins in this order of marine reptiles do not include more than five digits 

 and resemble those of the turtles (Chelone) amongst existing Reptiles ; hence 

 the name proposed, from aavfjos, a lizard, and irrepvl,. There are no post- 

 orbital and supratemporal bones f: the skull shows large temporal and other 

 vacuities between certain cranial bones, including a foramen parietale : there 

 are two antorbital nostrils : the teeth are simple, in distinct sockets of the 

 premaxillary, maxillary, and premandibular bones : they are very rarely pre- 

 sent on the palatine or pterygoid bones. The maxillaries are larger than the 

 premaxillaries. Limbs natatory ; with not more than five digits. There is a 

 sacrum of one or two vertebrae for the attachment of the pelvic arch in some : 

 there are numerous cervical vertebras in most. The pleurapophyses have 

 simple heads ; those of the trunk are long and bent. 



* This character is retained in all the subsequent orders except the Batrachia. 

 t These bones do not reappear in the subsequent orders. 



