COPE ON OWEN ON PYTHONOMORPHA. 309 



are not of ordinal value.* They might be wanting from Pythonomorpha 

 and present in Lacertilia without violating their ordinal boundaries. I 

 enumerate those which appear to be essential only. They are the fol- 

 lowing : — 



Subclass STEEPTOSTYLIOA. 



Order Pythonomorpha. 



1. The parietal bones are decurved on the sides of the cranium, and 

 are continuous with the alisphenoid and prootic elements. 



2. The ophisthotic is largely developed, and extends upward and for- 

 ward to the walls of the brain-case. 



3. A distinct element connects the squamosal with the parietal bone 

 above the opisthotic. 



4. The teeth have no roots. 



5. There is no sacrum. 



6. There is no sternum. 



7. The bones of the limbs possess no condylar articular surfaces. 



Of the preceding seven characters, the decurvature of the borders of 

 the parietal bones at the margins, and their continuity with the margins 

 of the prootic bone, is of importance as a character not found in the 

 Lacertilia and universal among Ophidia. Even in Aniellido3\ and in the 

 Amphisbcenia, the most snake-like of lizards, the lateral borders of the 

 parietals are free, and are separated by a fissure from the greater por- 

 tion of the prootic.f 



The opisthotic has a greater development than in lizards, where it 

 does not reach the brain-case upward. In the serpents, its contact 

 with the brain-case is well known. The existence of another element 

 lying on the opisthotic, first pointed out by Marsh, is an important 

 character. The anterior extremity of this bone enters into the side-wall 

 of the cranium below the parietal, occupying much the position of the 

 pterotic, and resembling, even more than the opisthotic, the suspenso- 

 rium of the Ophidia. Should this be a true homology, the aflanity to 

 the Ophidia is strengthened ; and should it prove to be a distinct ele- 

 ment, not found in either Ophidia or Lacertilia, the claims of the new 

 order to existence are maintained. In either case it is clear that the 

 Ophidian suspensorium is not the squamosal bone. 



The demonstration of my second assertion, *. e., that the Pythonomor- 

 phous order presents more points of affinity to the serpents than does any 

 other order, may be seen in the above list of characters. Professor Owen 

 doubtless believes with me that the Lacertilia are more nearly allied to 

 the Ophidia than is any other order, so that I only need to show that the 



*I have enumerated eleven subordinate characters on pp. 125-126 of my report, Hay- 

 den's Series, vol. ii. 



t See Proc. Acad.Phila. 1864, p. 230, for the osteology of this family. 



i Compare Professor Owen's figures of crania of Liodon, fig. 15, with Monitor, fig. 7, 

 and Python, fig. 13. 



