AVilliston.] Mosasaurs. 95 



prolonged prootic in front and the exoccipital behind, which em- 

 braces the suspensorium for much of its length. 19. The 

 anterior limbs are fins, with all the elements in a single plane ; 

 the radius incapable of rotation ; the humerus broad and flat. 

 20. There are probably no hind limbs. Of the above charac- 

 ters, the first eight are those of serpents ; the five characters 

 following the ninth are lacertian ; while the seventeenth is pe- 

 culiar, and not found in any existing order of reptiles. The 

 eighteenth is characteristic of the Sauropterygia." 



In 1875 i3 he defined the order Pythonomorpha as follows : 

 " 1 . The quadrate bone is attached to the cranium by a 

 ginglymoid articulation, admitting of free movement. 2. The 

 ribs are attached by simple articulations to single articular 

 facets, or diapophyses, springing from the bodies of the vertebrae. 

 3. There are two pairs of limbs, which form paddles, having the 

 elements arranged in one plane, and incapable of rotation or 

 flexure on each other. 4. There is no sternum. 5. The scap- 

 ular arch consists of scapula and coracoid only. 6. There is no 

 sacrum. 7. The pelvis consists of slender elements, of which 

 the inferior are nearly transverse, and meet, without uniting, 

 on the middle line below. 8. The opisthotic bone projects free 

 from the cranium as the suspensorium of the quadrate bone, 

 and is supported and embraced by a pedestal projecting from 

 the cranial walls, composed of the prootic in front and the ex- 

 occipital behind. 9. The stapes lies in a groove on the posterior 

 side of this suspensorium, and is produced to the os quadratum. 

 "10. There is no quadratojugal arch. 11. The parietal is de- 

 curved posteriorly, forming the cranial wall in front of the 

 prootic. 12. The brain chamber is not ossified in front. 13. 

 The squamosal bone is present, merely forming the posterior 

 part of the zygomatic arch. 14. The mandible is composed of 

 all the elements characteristic of reptiles : the articular and sur- 

 angular distinct ; the angular represented by its anterior por- 

 tion only ; and the coronoid present. 15. The atlas consists of 

 a basal and two lateral pieces only ; the odontoid is distinct, 

 and is bounded by a free hypapophysis, besides the hypa- 



43. Cretaceous Vertebrata, p. 112. — 



