THE KEPTILIAN CLASS OF THE MOSASAUKID £&, 683 



gnosed a genus distinct from Mosasaurus, for which he proposed the 

 name Platecarpus. In the study of all these fossils he became so 

 impressed with their ophidian characters, that he concluded to 

 raise the family Mosasauridae to the rank of an order in the class 

 Reptilia, for which he proposed the name Pythonomorpha. 



The Cretaceous formations in the west of the United States 

 yielding these and other instructive additions to the Mosasaurian 

 group have been classified by the accomplished geologists Meek and 

 Hay den. The lowest is a sandstone ; the second consists of chalk 

 and calcareous marl ; the third, including yellowish and whitish 

 chalks, is noted as the " Niobrara Epoch "*; the fourth and fifth 

 series are laminated shaly clays and sandy beds. Prof. Cope adds 

 a sixth series of "Lignite" or " Fort -Union beds." From the 

 Niobrara group have been obtained most of the American fossils 

 allied to Mosasaurus. Of these Prof. Cope has entered, in his richly 

 illustrated Report :- 



Of the genus Leiodon, 4 species ; 

 ,, „ Platecarpus, 10 species ; 

 „ „ Clidastes, 10 species; 



Sironectes, 1 species j 



and he remarks : — " These sea-serpents, for such they were, embrace 

 more than half the species found in the lime-stone-rocks in Kansas, 

 and abound in those of New Jersey and Alabama " f . 



And here I may remark that some fossils of the kind alluded to, 

 from a Neocomian or " greensand " formation in New Jersey, were 

 brought over by Prof. Henry Rogers, of Pennsylvania, and sub- 

 mitted to my examination in 1848. One was a basioccipital bone 

 of a reptile, about the size of the Mosasaurus Hoffmanni, Cuv. This 

 fossil being associated with characteristic teeth of the genus, together 

 with vertebras of the Mosasaurian type, and what at the time was 

 of especial interest, viz. phalanges of a limb of a natatory cha- 

 racter, I referred the series of fossils to that Cretaceous genus of 

 Reptilia £, and, from the modification of the teeth, to the American 

 species which had been noted by Goldfuss as the Mosasaurus Maxi- 

 miliani §. 



Now the basioccipital is one of the bones in Reptilia which 

 aid in determining the order, and perhaps minor group, in the class, 

 and this by the character of the exogenous process or processes 

 serially homologous with those termed "hyp apophyses" in the ver- 

 tebral centrums of the trunk. 



§ 2. Occipital Characters. — In Crocodilia the basioccipital hypapo- 

 physis is single, median, long and large ||, and extends the syndes- 

 motic connexion of this cranial centrum with the next centrum 



* Report &c. p. 16. 

 t Ibid, p, 45. 



t Quart. Journ. Geol. Soc. vol. v. 1849, p. 380, pi. x. 



§ " Der Schadelbau des Mosasaurus^ &c. in Acta Acad. Cses. Leop. -Carol. 

 Nat. Curios,' vol. xxi. p. 179 (1842). 

 || Anat. of Vertebrates, vol. i. p. 135. 



