56 



ME. C. W. ANDREWS ON THE SKULL AND 



odd bones referred to this species, but the following description is founded as far as 

 possible on the associated set, which is the type-specimen. 



The Skull and Mandible. (Plates XIV. & XV.) 

 The skull and mandible are in a wonderfully perfect state of preservation, and, now 

 the matrix has been removed, all the important details of their structure can be made 

 out. The skull has been slightly crushed, so that there is some dislocation of the 

 bones of the roof, and also a slight compression of the beak, but otherwise it retains 

 its original form. 



EiK. 1. 



oc.f 



Occipital surface of skull of PJiororhacos inflaius Ameghino. f natural size. 



l.r., lambdoidal ridge ; m.t., mammillar}" tuberosities ; oc.c, occipital condyle ; oc.f., occipital foramen ; 



p.p., paroceipital processes ; sf.r., supraforaminal ridge ; q., quadrate. 



The Occipital Begion (text-figure, above). — The occipital surface is remarkable for its 

 flatness, its great width from side to side, and the distinctness with which it is marked 

 off from the other regions. This last peculiarity is due to the great development of 

 the lambdoidal ridge (l.r.), particularly towards the sides. In its middle portion this 

 ridge merely forms the angle (of about 100°) between the occipital and dorsal regions, 

 but laterally it is produced outward, forming prominent lateral crests which are 

 continuous ventrally with the broad paroceipital processes [p.p.). These latter are 

 convex posteriorly, both from above downward and from side to side ; their inferior 

 angles extend somewhat below the occipital condyle, and are formed by the ventral 

 prolongations of the very well-marked supraforaminal ridges. These ridges run 

 downward and somewhat outward from the upper border of the foramen magnum {oc.f.), 

 and form the inner borders of the paroceipital processes, separating them from a 



