Cope.] 262 [January 20, 



Mosasaurus giganteus Soemmering. Lacerta gigantea Soem- 

 mering. Mosasaurus Hofinannii Mantell. M. Cmnperi Meyer. M- 

 helfi'icus Hall. 



Upper cretaceous; Belgium, Rliine-Prussla and England. 



MosasavLTUS gracilis Owen, British Fossil Reptiles. Upper 

 cretaceous, England. 



Mosasaurus Mitehillii D.dvay. Geosaurus MUchiUii DeKay. 

 ALlwitochebjs Mortoni Agassiz. Mosasaurus Cowperi and M. carol'men- 

 sis Gihbes. 



The ujiper cretaceous of the Eastern United States. 



In addition to the characters already pointed out, this species 

 differs from the M. 7nissuriensis, as follows, judging from the figures 

 and descriptions of Goldfuss. 



In il/. Mitehillii the prootic wraps over the opisthotic to its superior 

 face; in 31. missitriensis the exoccii^ital wraps over to the supei'Ior 

 face of the same bone. 



In inlssuriensis the squamosal forms a horizontal three-cornered ex- 

 pansion, and only touches the opisthotic behind. 



In Mitehillii the squamosal is largely Inferior, and has no superior 

 expansion. 



In Mitehillii the under face of the suspensorlum Is underwrapped 

 by the prootIc, in missuriensis by the exoecipital. Glenoid ca\ity two 

 thirds on squamosal in M. Mitehillii; not at all on squamosal in M. 

 missuriensis. 



Mosasaurus maximus Cope. sp. nov. 



This new species is indicated by a nearly perfect os quadratum, 

 several dorsal and cervical vertebra, including axis and atlas, a por- 

 tion of the mandible with probably numerous teeth. The latter have 

 not yet come into my hands. The remains indicate an animal of the 

 largest size, perhaps seventy-five feet in length. 



The quadrate bone, compared with those of two other species from 

 the New Jersey Green-sand, presents marked characters. Six quad- 

 rate bones of the j1/. J//?c7( ///a exhibit such constancy in the form as 

 vras to have been anticipated, while one of the third species, — per- 

 haps the M. depressus Cope, is quite different from both. Its proximal 

 extremity is sub-tripodal, the external angle being much longer than 

 that over the great ala, being in fact a process. In tlie M. maximus and 

 il/. Mitehillii, It is an obtuse angle, and that over the ala a process, 

 which is very large In the former, and small in the latter. The knob 

 just within the meatus of the ear Is very prouiineut in the M. depres- 



