1 1 44 CLASS REPTILIA. 



long, and have zygosphenal articulations ; the humerus is short ; 

 and the chevrons are anchylosed to the centra. Sironectes is an 

 allied genus from the same deposits, in which the chevrons are not 

 anchylosed to the vertebrae. Platy carpus 1 (Lestosaurus, Taniwha- 

 saurus), which is found in the Cretaceous of North America, New 

 Zealand, and perhaps Europe, differs from both the preceding 



Fig. 1047. — Frontal aspect ot the cranium of Platycarpus curtirostris ', from the Upper Cre- 

 taceous of North America. Greatly reduced, pmx, Premaxilla ; 7tix, Maxilla ; fr, Frontal ; 

 prf, Prefrontal. (After Cope.) 



genera by the absence of zygosphenes ; the chevrons being free 

 and the humerus (fig. 1046) short and broad. With the genus 

 Liodon, in which Professor Cope includes Tylosaurus (Rhino- 

 saurus) of Professor Marsh, we come upon forms attaining gigantic 

 dimensions, in which the body is proportionately shorter than 

 in the above-mentioned genera, and the vertebrae are always 

 without zygosphenes. In Liodon itself the extremity of the pre- 

 maxillae is devoid of teeth, and forms a cylindrical rostrum ; the 

 teeth are smooth and more or less laterally compressed ; the hu- 

 merus is long ; and the chevrons are free. It occurs in the Creta- 

 ceous of Europe, North America, and New Zealand. Hainosaurus, 

 again, of the Upper Chalk of Mons, agrees with Liodon in its eden- 

 tulous rostrum and free chevrons, but has teeth of three types. 

 Some of the teeth are subcylindrical, and others compressed, with 

 serrated cutting edges like those of Megalosaurus. The total length 

 of this huge Reptile is estimated at about 40 feet. The typical 

 genus Mosasaurus is definitely known from the topmost Cretaceous 

 of Maastricht in Holland, and the Cretaceous of North America ; 

 the type species from Maastricht having been made known to 

 science in the last century. It is characterised by the premaxillae 

 being toothed to their extremity ; by the teeth having their crowns 

 faceted and more or less compressed ; as well as by the greater 

 number of the chevrons being anchylosed to the vertebrae. The 

 fine skull of M. Camperi represented in the accompanying woodcut 

 was obtained from Maastricht previously to 1785, and is preserved 

 1 Amended from Platecarpus. 



