Stewart.] cretaceous Fishes. 281 



The prootics have been correctly interpreted by Professor Hay 

 as being the largest of the otic bones. They are irregular in 

 outline and extend from the groove for the hyomandibular 

 above to the parasphenoid below. Posteriorly they unite with 

 the opisthotic, but are not separated from the basioccipital by 

 the opisthotic, as Professor Hay has figured them in Tarpon at- 

 lanticus. 41 Just below the hyomandibular facets there is a large 

 foramen on each side, which, according to Professor Hay, trans- 

 mits the glossopharyngeal nerve. Just back of these foramina 

 there are large fossa\ the boundaries of which are formed by 

 the pterotics, opisthotics, and prootics. 



The sutures separating the lower portions of the opisthotics 

 from the basioccipital and the prootics are well defined, but the 

 ones separating them from the pterotics above are almost oblit- 

 erated, although I think they can be traced in one of our speci- 

 mens as extending downward just back of the articular face 

 for the hyomandibulars. They are small bones and do not 

 separate the prootics from the basioccipital, as mentioned above. 

 The basioccipital is deeply concave, and the exoccipitals are not 

 well defined in any of our specimens. 



The parasphenoid is triangular in section and forms a strong 

 lower axis of the skull. The posterior extremity of the bone is 

 deeply emarginate where it joins the basioccipital, a short dis- 

 tance in front of which it sends up a short process on each side 

 for union with the prootic. Extending outward from the sides 

 of the bone, just in front of the brain-case, there are two well- 

 developed transverse processes which are bluntly pointed and 

 directed slightly forward. At the base of each of these proc- 

 esses there are two foramina which, according to Crook, trans- 

 mit the facialis and trigeminus. Just above the transverse 

 processes there is a Y-shaped bone, called basisphenoid by Hay, 42 

 which unites with the prootic above. The anterior end of the 

 parasphenoid is somewhat broadened and bifurcated for union 

 with the vomer. The latter bone is not well defined in any of 



41. ZooL Bull., vol. II, No. 1, n. 28. 

 4J. 1. c, p. 82. 



19-vi 



