part 3] FEOM THE WEALD CLAY OF BERWICK ( SUSSEX). 287 



the jugal and postorbital, completing the outer boundary of the 

 relatively large temporal fossa. The upper limb of the squamosal 

 runs upwards to the parietals, forming with them the posterior 

 border of the temporal fossa ; it cannot be determined whether the 

 squamosals meet in the middle line above the parietals. 



The parietals {par.) form a A- shaped roof to the cranial 

 cavity; posteriorly (as just described) they are overlapped by the 

 squamosals : towards the middle of the temporal fossa they narrow, 

 and rise in the middle line into a high sagittal crest which is 

 interrupted by a rather large pineal foramen, situated about 

 opposite the hinder border of the orbits. In front of this the ridge 

 is continued forwards on to the frontal, and, at the level of the 

 front of the orbits (orh.), it is very prominent, and is separated 

 from those openings by a well-marked channel. On the left side 

 in this specimen there is an element uniting with the outer edge 

 of the frontals, and forming a rounded upper border to the hinder 

 part of the orbit : this is doubtless the post-frontal. Between this 

 element and the temporal arcade is seen the impression of another 

 bone, the postorbital; this probably united with the jugal 

 below, but the limits of these elements are obscure. 



On the right side the anterior border of the orbit seems to be 

 formed by a bar of bone (p-f.) curving up from the maxilla towards 

 the frontals (? prefrontals) ; it cannot be determined whether 

 this bone is entirely composed of maxilla, or M^hether it may in- 

 clude other elements, such as the prefrontals. 



The maxilla forms most of the lower border of the orbit; 

 on the palatal surface it widens out, and seems to have borne teeth 

 about as far back as the middle of the suborbital vacuity. In 

 front its suture with the palatine can be seen, but posteriorly its 

 relations with the jugal and other elements are obscure. 



The unfortunate loss of the anterior portion of the skull makes 

 it impossible to say to what extent the snout was elongated, and 

 renders comparison with other forms difficult. In a general way, 

 it may be stated that the temporal fossa is larger in proportion to 

 the orbit than in most Plesiosaurs. The region of the para- 

 sphenoid and the posterior interpterjj^goid vacuities seem to be the 

 most useful for purposes of comparison, the thin sharp edge of the 

 parasphenoid separating the vacuities being very characteristic. 

 In most Plesiosaurs this region of the parasphenoid is wide : for 

 example, in Plesiosaurus macrocephalus ^ it is broad, and has a 

 flattened ventral surface : this seems to be the case also in Crypto- 

 cleidus, Murcenosaurus, Tricleidus, DolicJiorJiynchops, and to a 

 less degree in BracTiauchenius, The skull of JKicrocleidus homalo- 

 spondylus (Owen) from the Upper Lias of Whitby approaches the 

 specimen here described in the form of its parasphenoid; but 

 differences in the skull and other parts of the skeleton exclude the 

 possibility of any near relationship. Unfortunately, the skull of 

 P. arcuatus is not known. In the nearly contemporary Branca- 



1 Q. J. G. S. vol. lii (1896) p. 246. 



