WILLISTON : NOTES ON SOME EXTINCT REPTILES. 251 



sas museum, disclosed them in four different skulls. In one 

 the bone lies transversely in the bottom of the supratemporal 

 fossa anteriorly ; in another, one was found impressed upon the 

 under surface of the parietal, also transversely. A third was 

 found by the side of the basisphenoid. In the fourth specimen, 

 fortunately, both bones were discovered lying side by side on 

 the under surface of a frontal bone of Platecarpus, with the 

 broad or flattened end lying over the two pits or depressions 

 for their attachment. These pits are toward the posterior end 

 of the frontal bone, on the sides of the median line, and nar- 

 rowly separated by the olfactory groove. They are clearly 

 shown in fig. 3, plate XXVI, as also in plates XII and XV of 

 the above-mentioned work. The other extremity of the bone 

 has not been found in position, but, by placing a well-formed 

 bone in position, this extremity is found to approach or meet 

 the rounded, conspicuous pit on either side of the base of the 

 presphenoid, at the anterior end of the sphenoid, and here is 

 doubtless where it belongs. The bone, as seen in the enlarged 

 figure, terminates below in a cylindrical and truncated ex- 

 tremity, which is either flat or cupped. The other extremity is 

 broad and flattened, with a transverse, curved sutural surface, 

 for lodgment in the frontal pits. The posterior border is 

 deeply concave ; the anterior border convex and subangulated 

 near the middle. The inner surface is more flattened than the 

 outer (the one shown in the figure) . The two bones lie parallel 

 with each other, almost touching, with only a narrow space be- 

 tween them above for the passage of the olfactory bulb. 



Because of this attachment to the frontal bone, it would seem 

 certain that the bone is the orbitosphenoid and not the ali- 

 sphenoid, especially so if the lower attachment is, as I believe 

 it to be, in front of the optic foramen. However, the same or a 

 similar bone is found among some lizards, though less com- 

 pletely ossified, and with feeble or no attachments. It is called 

 by Cope the "postoptic," provisionally : 



"The membranous wall of the brain-case anterior to the 

 petrosal contains an ossification which is of uncertain homol- 

 ogy. It reaches or approaches by its superior extremity the 

 frontal, and might hence be supposed to be the orbitosphenoid, 

 but this homology is vitiated by the fact that its inferior portion 

 passes behind the optic foramen. The latter position is that of 



