206 TEKTIAET VEETEBEATA OF THE EATtTM. 



by the apparently loosely united periotic {per.). The relations of the bones in this 

 region seem to be very similar to those found in Manatus, except that in the latter 

 genus the squamosal is not entirely cut off from contact with the supraoccipital. 



Beneath the periotic opening the post-tympanic portion of the squamosal unites 

 closely with the anterior face of the paroccipital region of the exoccipital, and in front 

 forms the posterior border of the external auditory meatus, the anterior boundary 

 of which is constituted by the slightly developed postglenoid process. The articular 

 surface (gl.) for the mandible is very broad ; it is slightly concave from side to side 

 and gently convex from before backwards, except where it runs on to the slight post- 

 glenoid ridge. The zygomatic process (zyg.) is very stout and is triangular in section ; 

 it is underlain anteriorly by a slender prolongation of the jugal. The parietals {pa.) 

 are large bones forming most of the cranial roof; posteriorly, as already mentioned, 

 they are separated in the middle line by a process of the supraoccipital, and laterally 

 they send back processes which thrust themselves between the squamosal and 

 supraoccipital, and help to form the large prominences of the lambdoidal ridge. From 

 the posterior angles of the bones a pair of not very well-defined supratemporal ridges 

 run forwards, first converging slightly, then running parallel to about the level of 

 the anterior border of the glenoid surface; in front of this they diverge considerably, 

 and finally become continuous with the hinder edges of the postorbital processes 

 of the frontals. 



Owing to the comparatively small development of the supratemporal ridges and 

 also to the slight inflation of the cranial portion of the skull, the roof is not nearly 

 so sharply marked off from the temporal fossae as in the later forms, even in Eosiren. 

 The ventral borders of the parietals unite with the squamosals posteriorly, then for 

 a short distance with the upper end of the alisphenoid {al.), and in front of this again 

 with the frontals, which they overlap in a squamous suture, running forwards in 

 a sharp angle on the supratemporal ridges. The frontals {fr.) are very wide, forming 

 the broad gently convex skull-roof in the region of the orbits, which they overhang 

 as large supraorbital plates. Posteriorly they join the alisphenoid and in front 

 of this their ventral edges seem to form the outer border of the groove for the optic 

 nerve. Their anterior border is notched for the reception of the hinder encis of the 

 nasals, between which they send a short triangular process. The nasals (na.) seem to 

 have been of considerable size, and overhung the narial opening (nar.) to some extent. 

 The opening itself is an elongated oval in outline, and its borders are formed by the 

 nasals behind and by the premaxillae in front and at the sides. The premaxillary 

 rostrum must have been bent down to a considerable extent, but in this specimen it 

 has been straightened out by the pressure to which it has been subjected, and the end 

 has been broken across the alveoli of the anterior incisors. The upper surface of the 

 rostrum in front of the narial opening is gently concave from side to side. 



The maxilla {mx.) is a greatly elongated bone ; the anterior edge of its palatine region 



