ICHTHYOPTEKYGIA 19i) 



temporal and other vacuities between the cranial bones : 

 a " foramen parietale," a single convex occipital condyle, 

 and one vomer which is edentulous. Two antorbital 

 nostrils. Vertebral centra, ossified, biconcave. Pleur- 

 apophyses 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 natatory ; 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 Ganoid fishes, the present ex- 

 clusively marine Eeptilia more directly exemplify the 

 ichthyic type in the proportions of the premaxillary 

 and maxillary bones, in the shortness and great number 

 of the biconcave vertebras, in the length of the pleur- 

 apophyses of the vertebras 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. 



It has been usual to unite the present with the following 

 order in the same group, called Enaliosauria or sea-lizards. 

 They were adapted for marine life, but breathed the air like 

 the Cetacea : they were, however, " cold-blooded," or of a low 

 temperature, like crocodiles and other reptiles. The proof 

 that the Enaliosaurs respired, atmospheric air immediately, 

 and did not breathe water by means of gills like fishes, is 

 afforded by the absence of the bony framework of the gill 

 apparatus, and by the presence, position, and structure of the 

 air-passages leading from the nostrils to the mouth, and also 

 by the bony mechanism of the capacious chest or thoracic- 



