0. P. Hay — Notes on species of Ichthyodeetes. 231 



and probably Xiphactinus, the opisthotic sends forward a pro- 

 cess below this excavation. 



A remarkable feature of the head of this genus is found in 

 the upward flexure of the forward part of the skull. At the 

 anterior end of the basioccipital there is formed an angle of 

 about 55° between the basal and the anterior parts of the 

 skull. This reminds us of the figure of a young tarpon pre- 

 sented by Dr. Shufeldt in his work on Amia (Ann. Rep. 

 Comm. Fish and Fisheries for 1883 (1885), pi. xiv). As regards 

 Tarpon it is to be noted that in the adult fish this angle is 

 greatly reduced, not exceeding perhaps 10°. 



It seems rather remarkable that neither among Cope 7 s speci- 

 mens, nor those of Crook, nor those belonging to myself is 

 there present an example of the premaxilla. Yet the surface 

 of the maxilla indicates plainly that a premaxilla was applied 

 to it, just as in Xiphactinus and Ichthyodeetes. I do not see 

 that it was relatively any smaller than in the two genera just 

 mentioned, although it was doubtless much thinner. 



While the skull in my possession is considerably crushed, 

 and somewhat distorted, I am able to say with some confidence 

 that the alisphenoids and orbitosphenoids were present and 

 that they were quite as extensive bones as they were in 

 Xiphactinus ; but better specimens are needed in order to 

 demonstrate their characters. 



There seems to have been a nasal. As such I interpret a 

 bone which is four or five times as long as wide, which lies 

 mesiad of the nasal cavity and which articulates in front with 

 the large ethmoid, while mesially it joins in part the ethmoid, 

 but principally the outer border of the frontal. 



Crook has figured a portion of the lower jaw. The depth 

 of this jaw in comparison with the maxilla is much greater 

 than in the typical species of Ichthyodeetes. The mandible 

 appears to possess the same composition as that of Xiphactin us, 

 viz., a dentary, an autarticulare and a dermarticulare, although 

 it is possible that the two latter are consolidated. I am not 

 able to find a distinct angulare. The cotylus for the quadrate 

 is situated on the inside of a broad process, as in Xiphactinus. 

 In my possession is the mandible of a large specimen of Gilli- 

 cus, to the inner surface of which are appressed the hyoidean 

 bones and the gill-arches. The hyoids and the gill-arches are 

 so confused that not much can be determined regarding them. 

 The hyoids were, however, very broad. A portion of a gill- 

 arch displays an armature of small teeth. The gill-rakers were 

 numerous, long, flat and wide, resembling those of Tarpon. 

 Some of them are 48 mm long and, at the base, 5 mm wide. They 

 were furnished with an armature of small teeth. The gill- 

 rakers of the anterior arch were evidently more rigid than the 



