94 University of Kansas Geological Survey. 



structure of the skull in its details, we are surprised to find here 

 a middle ground in which not only the peculiarities of the above 

 named genera, but indeed also those of most other saurians are 

 united, together with others which are peculiar to them and 

 distinguish them from all others" (p. 179). " From the fore- 

 going it is seen that the genus Mosasaurus has only the teeth 

 alveolae in common with the crocodilians and the bony sclerotic 

 ring with the fish-like saurians, but on the other hand is related 

 to the living lizards, and especially agrees with the Monitor" 

 (p. 188). 



In 1869 42 Professor Cope proposed for the reception of the 

 Mosasaurs the erection of a special order, which he called 

 Pythonomorpha, and for which he gave the following characters : 



"1. The teeth have no fangs. 2. There is merely a squamosal 

 suture between the maxillary and premaxillary. 3. The opis- 

 thotic bone projects free from the cranium, and is the suspen- 

 sorium of the os quadratum. 4. There is no columella. 5. 

 There is no symphysis mandibuli. 6. The parietal is decurved 

 posteriorly and unites with the alisphenoid, forming the cranial 

 wall in front of the prootic. 7. The subarticular and splenial 

 elements of the mandible are connected by articular faces. 8. 

 The vertebrae are very numerous, much exceeding 100, and 

 frequently present the zygosphene articulation. 9. The ab- 

 dominal cavity is long and surrounded by many short curved 

 ribs, which have simple heads and a free antero-posterior move- 

 ment on vertical articulating surfaces, and which commence 

 close behind the axis vertebrae. 10. The pterygoids are elon- 

 gate and bear numerous teeth, and in one type are free, except 

 at the extremities. 11. The brain-case is not fully ossified an- 

 teriorly. 12. Scapula and coracoid elements are present. 13. 

 The caudal vertebne are furnished with chevron bones. 14. 

 The squamosal bone is present. 15. The angular bone is dis- 

 tinct. 16. The os quadratum is movably articulated to the 

 opisthotic. 17. The os quadratum embraces and incloses the 

 meatus auditorius externus. 18. The opisthotic is supported by 

 a pedestal projecting from the cranial walls, composed of the 



42. Proceedings Bost. Soc. Nat. Hist., XII, 253. 



