SQUAMATA. 191 



apparently allied genera Pontosaurus and Aigialosaunis, from 

 the Upper Cretaceous of the Island of Lesina, Dalmatia, exhibit 

 a comparatively short neck with from 7 to 9 cervical vertebrae ; 

 and one specimen of Pontosaurus shows the complete hind limb 

 which is described as essentially Lacertilian, with the phalangeal 

 formula 2, 3, 4, 5, 4. The largest of the Upper Cretaceous 

 specimens from Istria and Dalmatia indicate species between 

 two and three metres in length. 



r 2. Pythonomorpha. 



The members of the second group of Cretaceous Squamata 

 are still more completely adapted for an aquatic existence than 

 the Dolichosauria. Most of them attain a large size, and they 

 seem to have usurped the place in the economy of nature left 

 by the declining orders of Sauropterygia and Ichthyopterygia in 

 Cretaceous seas. They must have had a very wide distribution, 

 remains being met with in Europe, North and South America, 

 and New Zealand. Their precise systematic position is un- 

 certain, but they seem to represent an early stage in the 

 evolution of the Squamata before the modern Lacertilia and 

 Ophidia had become differentiated. 



The skull in these aquatic reptiles is remarkably similar in 

 general aspect to that of certain lizards such as the Varanidse, 

 but the pterygoid bones bear teeth like those on the margin of 

 the jaw. All the teeth are large and conical, fixed by tumid 

 bases to the oral border of the supporting bone. The pre- 

 maxillae and nasals are fused together into a simple rostrum ; the 

 superior temporal arcade remains; and a pineal foramen is 

 always present. The vertebral centra are all procoelous, and 

 there is no sacrum ; traces of a zygosphene-zygantrum articula- 

 tion are observed in some genera. Each chevron bone in the 

 tail articulates only with its own centrum. The pectoral arch 

 seems to be nearly always destitute of clavicles, though rudi- 

 ments may occur and an interclavicle has occasionally been 

 detected; the sternum appears to have been rarely calcified and 

 perhaps never truly ossified. Both pairs of limbs are present 

 and modified into paddles, the digits being destitute of claws 

 and slightly lengthened by an increase in the number of 



