42 Bulletin American Museum of Natural History. [Vol. XIX, 



be observed, in the type of the species the anterior edge of 

 the presphenoid is but Httle in front of the middle of the para- 

 sphenoidal triturating surface; while in the specimen here 

 described the presphenoid comes much farther forward. 

 These differences may be individual, however. 



As will be observed, the supraoccipital lies some 25 mm. 

 to the right of the basioccipital, having been crushed to the 

 right and downward. This shows that the skull must have 

 been elevated at least that many millimeters above the fora- 

 men magnum, a conclusion which is confirmed by the skull 

 described by Dr. Loomis. About 20 mm. in front of the 

 hinder extremity of the supraoccipital begins an abrupt de- 

 pression. It is about 10 mm. wide, and extends well forward 

 on the frontals. From Fig. 28 the position and boundaries 

 of the various bones may be seen. In general, these agree 

 with those shown in the specimen described by Loomis as 

 Thryptodus zitteli {op. cit., pi. xxi, fig. i). On the left the 

 opisthotic, sphenotic, and hinder part of the frontal are in 

 their natural positions and form the border of the skull. On 

 the right the squamosal has been flexed downward at right 

 angles with the surface of the skull. The border of the fron- 

 tal on the left has probably been bent downward somewhat 

 more than in life. 



Figure 28 presents the skull as seen from below, only the 

 outlines of the presphenoid {p. sp.) and parasphenoid {par.) 

 being drawn. This bone will be described below. The ob- 

 server must imagine himself as turning it to the left until it 

 stands at right angles with the paper, and has the triturating 

 surface {par.) facing him. 



In this figure the prootics are drawn as meeting in the mid- 

 line. This cannot be certainly affirmed; but the appearances 

 are to that effect. There appears to have been a considerable 

 excavation of some sort beneath the projecting edge of the 

 squamosal and outside of the hyomandibular articulation. 

 The alisphenoids are large, agreeing with those of Dr. Loomis 's 

 figure of A. altus. We come now to the bone called by Dr. 

 Loomis the orbitosphenoid. It appears to agree with the 

 bone so-called by Parker (Philos. Trans. Roy. Soc, CLXIII, 



