194 REPTILIA. 



phalanges. There are sclerotic plates round the eye, but the 

 dermal armour is apparently never more than a covering of 

 small scaly granules. 



Mosasaurus (fig. 117 c F, i). The typical genus was first discovered 

 in the Upper Cretaceous of Maastricht, in the valley of the Meuse, and 

 hence named Mosasaurus. The massive jaws are provided with teeth as far 

 as their anterior extremity, and sclerotic plates are present. The vertebrae 

 are more than 130 in number, 7 being cervical, 39 dorsal, 12 lumbar, and 

 the remainder caudal. The centrum of the atlas is fused with that of 

 the axis to form its odontoid process, and both these vertebrae bear 

 neural arches. The other vertebrae are all similar in type, the neural 

 arch always fused with the centrum and bearing zygapophysial facettes 

 but no zygosphene or zygantrum ; the zygapophyses, however, are more 

 or less rudimentary in the hinder dorsal and caudal regions. The axis, 

 other cervical vertebrae, and the dorsal vertebrae bear ribs, which become 

 longest on the 18th dorsal; the centra of the lumbars and caudals exhibit 

 only transverse processes. Between the atlas and the basi-occipital there 

 is a small proatlas in the form of a free hypapophysis ; the atlas itself and 

 also the other six cervicals have a separate hypapophysis. The chevron 

 bones in the tail are fused with their respective centra, at least in its 

 middle and hinder portions. The fore limbs have not been satisfactorily 

 observed, but the hind limbs are known by specimens completely pre- 

 served in a hard matrix, and the arrangement of their bones is thus 

 definitely ascertained (fig. 117 i). The femur is a little longer than the 

 tibia, while the tarsus and foot are about four times as long as the 

 latter; none of the bones exhibit condyles, but are merely apposed by 

 flat articular facettes. The tarsus comprises only three bones, which are 

 displaced towards the fibular side, so that the first metatarsal articulates 

 directly with the tibia. Digits I iv, are complete, and exhibit phalanges 

 to the number of 6, 5, 5, 4 ; digit v is represented merely by its displaced 

 and stunted metatarsal. The pelvic bones are comparatively small and 

 slender, all meeting in the acetabulum, and the pubis is pierced by a small 

 foramen. The typical species, Mosasaurus camperi, from the Upper Cre- 

 taceous (Danian) of Maastricht, probably sometimes attained a total 

 length of 15 metres. M. lemonnieri, from the Upper Cretaceous (Upper 

 Senonian) of Mons, Belgium, is known by more nearly complete skeletons 

 only 5 metres in length. 



Platecarpus (fig. 117 A, B) closely resembles Mosasaurus, and is repre- 

 sented by nearly complete skeletons from the Cretaceous of Kansas, 

 U.S.A. The skull (figs. 117 A, B) is not much depressed, and teeth 

 extend to the extremity of the jaws. There are 7 cervical vertebrae, 

 23 dorsals, and over 80 caudals; the zygapophyses are well-developed, 

 but the zygosphene-zygantrum articulation is almost or completely 

 wanting. The centrum of the atlas is fused with that of the axis to 



