106 A REVISION OF THE COTYLOSAURIA OF NORTH AMERICA 



spine in the middle posteriorly is intercalated in the angle between the inner ends of 

 the postparietals, but there is no sutural attachment. Anteriorly the two sides of the 

 supraoccipital diverge in the form of zygapophyses, with an emargination between 

 them exposing the cerebral cavity. From the median posterior spine a ridge runs 

 outwards to each 'zygapophysis'. In front of each lateral projection, the prootic, 

 distinguished suturally, descends in a rounded margin to form the optic notch. 

 In front of these optic notches there is, on either side, a thin, vertical plate, attached 

 either to the prootic or basisphenoid below the meeting in the middle above, leaving 

 an opening of rather small size between them. The upper end of these plates is frac- 

 tured, but it is very evident that, in position, relations, and shape they agree quite 

 well with similar bones bounding the cerebral cavity in most lizards, a small bone, 

 usually lost in the macerated skull, whose homology is not well understood. Since 

 their position is in front of the optic nerve it would seem to preclude the possibility 

 of their being alisphenoids. These elements in the Mosasaurs I have identified as 

 orbitosphenoids (see University of Kansas Geological Survey, vol. iv, pi. xxix, f. 5; 

 Kans. Univ. Quarterly, vol. xi, p. 249), but neither identification is quite satisfactory. 



"The upper oblique surface of the pterygoid wings is concealed posteriorly by 

 the quadrates. In front of the quadrates, and occupying nearly the whole extent of 

 their margin and the upper half of their externo-superior surface, are the elongated 

 and oval epipterygoids. They continue the acclivity of the pterygoid wings on 

 the outer side a little more steeply, ending in an obtuse point a little back of the 

 orbitosphenoid plates, which touches, but is not suturally united with, the parietals 

 above. These epipterygoids are broader in front, where they come in contact with 

 each other over the pterygoids. The quadrates in the larger specimens, and also 

 in one of the smaller, are preserved nearly or quite intact, and in their natural re- 

 lations. They unite with four bones only, the pterygoids by a very broad and loose 

 union, as shown in fig. 2, plate 12 (of this paper), with the outer ends of the paroc- 

 cipitals, as also shown by the dotted lines in the same figure and in fig. 3, plate 12 

 (of this paper), and by their posterior everted articular margin with the outer 

 extremity of the postparietals and much more extensively with the ' epiotics ' near 

 the cranial wall. The thin, expanded proximal plate of the quadrate, as shown in 

 fig. 3, plate 12 (of this paper), narrows into a distinct neck, chiefly by a groove 

 which winds from the under side about the hind margin a little above the articular 

 extremity. The notch thus formed is clearly the auditory notch, corresponding to the 

 notch of foramen in the quadrate of the Mosasaurs and lizards; and possibly also 

 it corresponds with the so-called quadrate foramen of the Pelycosauria. Doubt- 

 less the Cotylosaurta had a small external ear situated nearly as it is in the lizards, 

 above the angle of the mandible. The articular surface of the quadrate for the 

 mandible is oblique to the plane of the bone, so as to look more nearly downward 

 in the normal position of the quadrate. Its outer side projects into a rather narrow 

 process, but does not touch, much less articulate with, the roof bones. 



"The mandibles, in comparison with the skull, are stout and heavy bones, and 

 amply attest the predaceous habits of the animals. They are slightly expanded in 

 front, where they meet in a short symphysis, heaviest and stoutest just back of the 

 orbits and broadest also here. They are nearly straight or gently incui^ved anteriorly 

 turned inwards in a broad cui^ve behind. The splenial bones unite in a median 

 symphysis in front and extend back nearly to the articular, leaving a broad, elongate 

 open cavity on the inner side from immediately back of the orbits. They also 

 form a part of the lower margin of the mandible, visible from below as far back as 

 the middle of the orbits, having between them and the hinder end of the dentary, an 

 elongate and acute projection of the angular. The suture between the angular and 



