Structure of the Fossil Saurians. 343 



Crocodile. The long beak is armed with numerous teeth which 

 stand in a common channel. The teeth are conical and pointed, 

 and differ remarkably from each other in the different species. 

 There were, probably, no palatal teeth. The apparatus of 

 breathing was adapted for elastic air, since nothing similar 

 to gills has been observed. The number of vertebrae occa- 

 sionally exceeds 100. The form of the vertebrae is striking, 

 considered as belonging to a Saurian animal, being similar to 

 those offish. Both surfaces are comparatively very concave, and 

 the length of the vertebra? is small in proportion to their di- 

 ameter. The ribs are inserted with a head, and an elevation 

 in the vertebral processes adapted to this purpose. All the 

 vertebras from the head to the pelvis are furnished with ribs. 

 The ribs are long, and united oppositely by ribs of the ab- 

 domen, probably in a similar mode to the Cameleon and 

 Anolis. The sternum and the scapula are essentially those of 

 the Monitor and Ornithorhynchus; more broadly and more 

 strongly, and I might say more pelvis-like, developed, since the 

 pelvis itself is neither so strong nor so large. The single parts 

 of the latter have not yet been sufficiently investigated : the 

 hinder limbs were smaller and weaker than the anterior. The 

 swimming apparatus consists, both in the hands and feet, of 

 rows of small and flat bones, similar to those of the Dolphin : 

 these, however, were more numerous, and placed nearer each 

 other. The Ichthyosauri were no better enabled to creep 

 about on land, than Mammalia with limbs adapted for swim- 

 ming can now do. The tail is about a fourth part shorter 

 than the length of the trunk ; and the head consists of about 

 the fourth part of the total length. The structure of the 

 cervical vertebrae gives this creature the appearance of having 

 no neck. 



As yet the following species only of the Ichthyosaurus have 

 been distinguished, the differences of which chiefly relate to 

 the bones of the head, the teeth, the form and dimensions of 

 the vertebrae, the number of the caudal vertebrae, &e. 



a. Ichthyosau'rus communis Dc la Beche et Conyb. 

 According to Conybeare, the length of this species is from 

 5 to 15 feet. The teeth have a crown, which is conical and 

 moderately pointed, somewhat bent and deeply striated. 



b. Ichthyosau'rus tenuiro'stris De la Beche et Conyb. 

 The teeth are more slender, and the beak is longer and 

 thinner. This species does not attain one half the size 

 to which the following arrive. In one individual of 3£ 

 French feet, the head and tail occupy each a foot. The 

 neck is so short, that it can scarcely be observed. The fore 



c c 4 



