1869.] 253 [Cope. 



ities of Mosasaurus," this combination, is " incongruous," and assigns 

 the bones mentioned by Leidy, to the turtles and Plesiosauria re- 

 spectively. 



I, however, believe that Leidy has correctly assigned such limbs to 

 the two species that came under his observation; and I add the evi- 

 dence derived from another species of Mosasaurus, and from one of 

 Clidastes, as entirely confirmatory of it. On the other hand I am 

 unable to assign hind limbs to any of the species of the order. 



The characters of the order are as follows : — 



1. The teeth have no fangs. 



2. There is merely a squamosal suture between the maxillary and 

 premaxillary. 



3. The opisthotie bone projects free from the cranium, and is the 

 suspensorium of the os quadrature. 



4. There is no columella. 



5. There is no symphysis mandibuli. 



6. The parietal is decurved posteriorly and unites with the 

 sphenoid, forming the cranial wall in front of the prootic. 



7. The subarticular and sphenial elements of the mandible are 

 connected by articular faces. 



8. The vertebrsa are very numerous, much exceeding one hundred, 

 and frequently present the zygosphen articulation. 



9. The abdominal cavity is long, and is surrounded by many short, 

 curved ribs, which have a free antero-posterior movement on vertical^ 

 articulating surfaces, and which commence immediately behind the 

 head. 



10. The pterygoids are elongate and bear numerous teeth, and in 

 one type are free, except at the extremities- 



11. The brain case is not fully ossified anteriorly. 



12. Scapular and coracoid elements are present 



1.3. The caudal vertebras are furnished with chevron bones. 



14. The squamosal bone is present. 



15. The angular bone is distinct. 



16. The OS quadratum is movably articulated to the opisthotie. 



1 7. The OS quadratum embraces and encloses the meatus auditorius 

 cxternus. 



18. The opisthotie is supported by a pedestal projecting i'rom the 

 cranial walls, composed of the prolonged prootic In front, and the 

 exoccipital behind, which embniees the suspensorium for much of ita 

 leufrth. 



