﻿45 83 



hears laterally a sharp, prominenl edge which is continued on to the pterotic; after 

 a short hreak several sharp ridges appear again on the orbital margin of the fron- 

 ta)s; they collect into one ridge which anteriorly runs out on the nasal towards 

 the tip of the snout and posteriorly spreads over the broad part of the frontal. 

 Essentialh' the same bones are seen from the lateral aspect of the skull (PI. II, 

 fig. 2); the postfrontals {pf) are naturally more distinct, provided with a fairly long 

 postorbital process, which at its end (almost) meets the liyomandibular; of the 

 prefrontals [prf) only quite a small part is seen between the [)osterior margin of 

 the nasal opening and the orbit, bounded above by the frontals, below by the 

 preorbilals (ao). The last {ao) overlaps it on the outer side and forms the part 

 seen of the front and lower boundary of the orbit, reaching back to the preoper- 

 culum ; in front the preorbital forms the thin bridge under the nasal opening and 

 joins on to the nasal a little in front of this. The nasal is very long; posteriorly 

 it forms the anterior margin of the nasal opening and somewhat further forward 

 it projects up on to the upper side of the snout in order to meet the nasal of the 

 opposite side in a suture, then separates again from this and follows its side of 

 the vomer nearly to the tip of the snout. 



The posterior surface of the skull (tig. '26) shows as 

 in Ainphisile the two exoccipitals (eo) meeting one another 

 round the foramen (this has not been made very clear in 

 the figure); though under their margins the supraoccipital 

 also reaches to the foramen; in each exoccipital there is a 

 deep groove (gr) for articulation with the articular process 

 on the first vertebra. About half the epiotics (ep) are seen 



on this surface. The posttemporal (pt) forms a groove for n.,.„;»,K'.r. skuiiimmiuhind. 

 the supraclavicle (II) at its junction with the exoccipital. ™i;'3V.Vg?.;;j;\!;;'i;|^™^^^ 

 The characteristic hollows on the posterior surface, present "' '''^'''/)(Tp<'««ümpoi:i[''''''''^' 

 especially in A. strigata, are also faintly indicated here. 



Viewed from the under surface the skull is broader than in Amphisile but as in 

 this the under surface is distinctly angular anteriorly and the parasphenoid forms 

 a similar, blunt angle under the [)osterior part of the orbit; it is also hollowed 

 out ventrally in front of this in a similar manner. The pterotic is also the most 

 prominent bone on the cranial surface in Centrisciis and likewise separates the 

 exoccipitals from the proolic, forming ventrally a suture with the basioccipital. 

 The prootic forms with its front portion the lower part of the orbital wall of the 

 cranium; here the prootics of the two sides meet in the middle line and roof over 

 a deep canal for the eye muscles (myodoma), which is bounded laterally and 

 below by the parasphenoid and continues posteriori^' for a good distance into the 

 basioccipital. (A basisphenoid, as given by Starks, I have not been able to find). 

 Above the prootic the posterior wall of the orbit is formed by a small alisplienoid 

 and a quite insignificant orbitosphenoid as well as by the postfrontal. 



The vomer as in Amphisile is thread-like posteriorly under the middle of 



