ORDER SQUAMATA. 



1 145 



in the Paris Museum. This species is estimated to have attained a 

 length of 25 feet. Closely allied to Mosasaurus is Pterycollasaurus, 

 which is, however, readily distinguished by the complete union of 

 the pterygoids in the middle line — a feature unknown elsewhere 



Fig. 1048. — The imperfect skull of Mosasaurus Camperi; trom the Upper Cretaceous of 

 Maastricht. Much reduced. The displaced bone in the left bottom corner is the left pterygoid, 

 the corresponding bone of the opposite side being in its natural position above. 



in the whole order. The only known species is P. Maximiliani, 

 of the Cretaceous of Brazil. Finally, the genus Baptosaurus, of the 

 Cretaceous of North America, is distinguished from all other genera 

 by the complete union of the haemal spines of the cervical vertebrae 



Fig. 1049. — Left lateral and upper view of the skull of Boa. p}>ix, Premaxilla ; na, Nasal ; 

 pr, Prefrontal ; fr, Frontal ; po, Postfrontal ; pa, Parietal ; pc, Prootic ; so, Squamosal ; qu, 

 Quadrate ; pt, Pterygoid ; tr, Transverse ; 7iix, Maxilla ; ar, Articular ; de, Dentary. 



with the centra. The Mosasaurs attained their maximum devel- 

 opment at a time when the Ichthyosaurs were on their decline. 



