CRETACEOUS FORMATIONS. 21 



affinities of the genus, in the presence of a large oblique ''foramen parietale" 

 between the frontal and parietal bones (Tab. IV, fig. 1, p ). 



The parietal bone (7) is much compressed, and developes a sharp and rather lofty 

 median crest behind the foramen ( p ), which crest divides the temporal fossae {t, t). 

 Behind this crest the parietal bone expands transversely, and assumes a tri-radiate 

 form, the two transverse rays uniting with the mastoids (8, 8). These are very 

 powerful bones, bounding the outer and back part of the temporal fossa? ; they 

 are smooth and slightly convex above, rough and slightly concave at the back 

 part near the angle, where a surface is thus formed for the attachment of some 

 powerful muscle. The part of the mastoid which curves forward from the angle 

 to form the back part of the zygomatic arch, becomes compressed, and terminates 

 above in a ridge (,•). The substance of the mastoid is extensively excavated, appa- 

 rently for the upper part of the acoustic chamber. 



The frontal bone (11) is overlapped behind by the parietal, and appears to 

 have been divided by a median "harmonia," or smooth suture; the receding 

 halves of the frontal behind, as they pass beneath the parietal, form the forepart 

 of the foramen parietale. The back part of the foramen is formed by a notch 

 in the forepart of the single and undivided parietal. The canal from the fora- 

 men extends obliquely downward and backward. The long diameter of the 

 foramen is 1 inch; the breadth of the back part of the cranium is 16 inches ; the 

 breadth of the back part of each temporal fossa is 6| inches. The power of the 

 muscles acting upon the lower jaw must have been very great. 



A portion of a symmetrical bone, 10 inches long, which formed the upper 

 median part of the face, anterior to the orbits, represents part of an undivided 

 nasal bone (is) and shows that bone to have been long, narrow, straight longi- 

 tudinally, convex transversely above, as if the upper part of the face had been 

 traversed by a low, obtuse, median rising. 



In most of these characters may be discerned a closer affinity to the Plesio- 

 sauroid than to the Crocodilian type. 



The expanse of the temporal fossae equals that in the Plesiosauri and Teleo- 

 sauri, but no species of the latter genus of Crocodilia has presented the " foramen 

 parietale," whilst it is a constant character in the Plesiosauri, Ichthyosauri, 

 and Labyrinthodontia ; many of the modern lizards also present the same 

 foramen. The portion of the upper maxillary bone, figured of the natural 

 size at fig. 2, Tab. I, shows the same obliquity of the separate sockets of the 

 teeth as exists in those at the forepart of the bone in certain Plesiosauri, and 

 the small separate foramina (0, 0), at the inner and back part of the large alveoli, 

 which had been perforated by the summits of the successional teeth, are of 

 plesiosauroid character. I have seen portions of jaws of Plesiosaitrus 

 megacephalus in which the appearance of a double row of teeth was caused by 



