fixed to the cranium, and there is a large parasphenoid. There are large prefrontals, but the frontals are very small. The very numerous teeth are large and conical, and are placed in continuous grooves without being ankylosed to the bone. They are confined to the jaw-bones. [Illustration FIG. 32. LATERAL (BELOW) AND DORSAL (ABOVE) VIEWS OF THE SKULL OF AN _Ichthyosaurus_. (Modified from Deslongchamps.) 1. premaxillae. 2. maxillae. 3. nasal. 4. prefrontal[1]. 5. frontal. 6. postfrontal[74]. 7. anterior nares. 8. orbit. 9. supratemporal fossa. 10. interparietal foramen. 11. parietal. 12. squamosal. 13. supratemporal. 14. quadratojugal. 15. sclerotic ring. 16. postorbital. 17. jugal. 18. lachrymal. 19. dentary. 20. articular. 21. angular.] The ribs are long, and the anterior ones have capitula and tubercula. There is no sternum, but the ventral body wall is strengthened by a complex system of abdominal splint ribs. The pectoral girdle is strongly developed, the scapulae are narrow, the coracoids broad, and meet ventrally without overlapping. There are probably no precoracoids, but clavicles and a T-shaped interclavicle are well developed. The limbs are very short, and completely modified into swimming paddles. The humerus and femur are both short, while the radius and ulna, tibia and fibula are generally still further reduced to the form of short polygonal bones. The digits are formed of longitudinal series of very numerous small bones. The number of digits is five, but there sometimes appear to be more owing to the bifurcation of certain of them, or to the addition of marginal bones, either to the radial or ulnar side of the limb. The humerus has no foramen, and both humerus and femur are unique in that they are distally terminated by concave surfaces instead of by convex condyles. The pelvic limb is much smaller than the pectoral. The pelvis has no bony connection with the vertebral column, and all the component bones are small and rod-like. The Ichthyosauria are confined to beds of Secondary age and by far the best known genus is _Ichthyosaurus_. _Order 5._ RHYNCHOCEPHALIA. This order includes the living _Sphenodon_ (_Hatteria_) and various extinct forms. The general shape of these animals is lizard-like and the tail is long. The vertebrae are amphicoelous or sometimes nearly flat, and the notochord sometimes persists to some extent. _Proterosaurus_ differs from the other members of the order in having opisthocoelous cervical vertebrae.