114 



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 scapular 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 suspenso- 

 rimn of the quadrate bone, and is supported and embraced by a pedestal pro- 

 jecting from the cranial walls, composed of the prootic in front and the exoc- 

 cipital behind. 



9. The stapes lies in a groove on the posteriorside of this suspensorium, 

 and is produced to the os quadratum. 



10. There is no quadrato-jugal arch. 



11. The parietal bone is rlecurved 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 rep- 

 tiles: the articular and surangular distinct; the angular represented by its 

 anterior portion only ; and the coronoid present. 



15. The atlas consists of a basal and two lateral pieces only; the odon- 

 toid is distinct, and is bounded by a free hypapophysis, besides the hypapo- 

 physis of the axis. 



16. The caudal vertebrae support chevron-bones. 



17. The teeth possess no true roots. 



The free quadrate bone and simple costal articulations at once refer this 

 order to the Streptostylicate. division of the Replilia, which embraces only the 

 three orders of Laccrt'dia, Pythono?norpha, and Ophidia. There arc several 

 characters, however, in which it resembles some orders of one other primary 

 group, viz, the Synaptosauria, which embraces the Sauropterygia, Testudi- 

 nata, and Rhynchocephalia. 1 In the absence of sternum, it resembles tortoises 

 and Plesiosaurs, and differs from lizards. It resembles the tortoises in the 



1 See Proceedings of the Amci icau Association for the Advancement of Science, vol. XIX, p. 



1-T". 



