CROCODILIANS, LIZARDS, AND SNAKES. 405 



■ Its strong ijarietoqiiadrate arcli supports a horn or tuberosity, and 

 iiu most of the species the middle of the posterior border supports 

 the same. The occipital is broadly articulated with the parietal in P. 

 donglassii and P. coronatnm; in the former loosely, in the latter closely. 

 In P. coniutum it aifords a narrow but firm support for the parietal. 

 Paroccipital small, visible from behind. The postfrontal is visible as a 

 ^rudiment in P. douglas.sii, but it is apparently coossified in the other 

 two species. Tlie postorbital is slender, expanding below for union 

 {with jugal and supratemporal. The former bears two sharp tuberosi- 

 ties in P. coronafKm, and the supratemporal two. In P. cornutum there 

 is none on the jugal, but there are three on the supratemporal; and in 

 \\P. douglmsii the arrangement is similar. Owing to the inferior posi- 

 tion of the supratemporal, the quadrate is oblique forward and down- 

 ward. It presents one conch, the external. The vomers are short, and 

 are separated from each other for the posterior half or more of their 

 :leugth by a hiatus, which continues posteriorly of about equal width 

 [between the palatine and pterygoid pairs. The latter are short, wide, 

 'and flat, and the palatine foramen is small; least and oval in P. coro- 

 \natum; small and round in P. cornutum; larger and elongate in P. 

 \douglassii. The ectopterygoid is decurved at its inner extremity. The 

 presphenoid is wanting, and the suture between the sphenoid and the 

 ;basioccipital is persistent. The supraforaminal part of the petrosal is 

 ivery short, and the infraforaminal part is not much produced, and has 

 'a wide inferior groove. The epipterygoid originates behind the ecto- 

 'pterygoid process, and has the peculiarity among Iguanid;e of not reach- 

 ing the parietal, but of resting on the anterior border of the petrosal. 

 The occipital condyle shows traces of its tripartite composition. The 

 postoptic is curved and simple and does not reach the frontal bone. 

 The latter is grooved on the middle line below. 



I The groove of Meckel's cartilage is open throughout in P. cornutum 

 |md P. coronatum and distally only in P. douglassii. The coronoid is 

 'lot produced liorizontally on the external face of the mandible, and the 

 ilentary is not i)roduced beyond its posterior border. This element has 

 |i reflected inferior border in the P. cornutum which is acutely dentate 

 Posterior to the middle, characters absent from P. coronatum and P. 

 'douglassii. In P. douglassii the surangular is not coossified with the 

 'irticular, while it is so united in the other two species. The angle is 

 lihort, and is directed downward and obliquely inward. 



The basihyal is wide and is ossified, and the second ceratobranchials 

 ire very short and widely separated. The hypohyals are short and 

 larry the ceratohyls on their extremities. ISTo expansions of lateral 

 ilements. 



The vertebra; have no zygosphen articulation, but the prezygapophy- 

 ical facet is carried upon the side of the neurapoi)hysis at an angle with 

 he usual position. This furnishes the initial step in the production of 

 1. zygosjihen. I find five cervical intercentra in J', cornutum and P. 



