690 PROP. OWEN ON THE RANK AND AFFINITIES IN 



Prof. Cope figures the perforate parietal and portions of its pos- 

 terior bifurcation in a fragment of skull of a Mosasaur, which he 

 refers to a genus Platecarpus (op. cit. pi. xvi. fig. 4) * : he also figures 

 a portion of skull showing the postfrontal and part of the backwardly 

 extending long and slender squamosal, in the Mosasaur which 

 he refers to a genus Clidastes (op. cit. pi. xvi. fig. 1). The cranial 

 characters in European examples of Mosasaur and Leiodon, thus 

 corroborated by transatlantic fossils, are decisive evidences for 

 Lacertian, and against Ophidian, affinity. 



The cranial cavity or brain-chamber is unclosed anteriorly by 

 bone in Lacertilia ; in Ophidia (Python) the bony parietes of the 

 brain-chamber are continued anteriorly to the outlets of the olfac- 

 tory nerves, closing the chamber elsewhere, in front. Prof. Cope 

 gives, as the 12th character of his Pythonomorpha : — " The brain- 

 chamber is not ossified in front "f. But this is a Lacertian character 

 and is adverse to Pythonic affinity. 



His 10th character is : — " There is no quadrato-jugal arch." But 

 in no Reptile does the jugal or malar bone join the quadrate or 

 tympanic bone. 



In some Lacertilia (Monitor, Varanus, e. g.) the malar bone, after 

 forming the lower part of the orbital frame, stops short ; and the post- 

 frontal, 12, intervenes between it and the squamosal, 27. But in 

 the majority of lizards the malar does complete the zygomatic 

 arch with the squamosal, either directly or by interposition of part 

 of the postfrontal. The position of the zygomatic (malo-squamo- 

 sal) arch is thus at a higher level along the side of the cranium 

 than in the Crocodilia, Aves, and Mammalia ; and the Mosasaurus 

 shows the elevated position of the arch as in Lacertilia. But in 

 the Ophidia the z)^gomatic arches, by whatever name they may be 

 called, are altogether wanting. 



Prof. Cope defines a u 13th" character of his Pythonomorpha as 

 follows: — "The squamosal bone is present, merely forming the 

 posterior part of the zygomatic arch " (ib. p. 114). I am not, how- 

 ever, cognizant of any Vertebrate, recent or fossil, in which it forms 

 any other part of the arch. Meanwhile the fact remains that the 

 squamosal is wanting in all Ophidia : and thus the Mosasaurian 

 evidences from the Cretaceous series of the "Western States confirm 

 the strongly distinctive character exemplified in our European 

 fossils. The homologous bones being marked by the same numbers 

 in fig. 8 (from a skull of Python sebce, nat. size), the comparison 

 with figs. 6 and 7 needs no other guidance. 



§ 4. Tympanic bone — The tympanic bone, in the Breda Collection, 

 of Mosasaurus Hoffmanni — the type of the genus and family of 

 Mosasauroids — which is the subject of the following description, is 

 of the left side (figs. 9-12). Its length is six inches 8 lines, its 

 breadth 5 inches ; the longitudinal extent of the proximal, or mas- 



* In Platecarpus curtirostris, pi. xvi. fig. 4, and, again, in Plat, ictericvs, 

 pi. xvii. fig. 3. 

 t Op. cit. p. 114. 



