28 



HAY. 



[Vol. II. 



The head of this genus has been described by Cope {Ci'et. 

 Vert., pp. 183, 191), by Newton {Qnar. Journ. Geol. Soc, vol. 

 xxxiii, p. 505), and by Crook [Palacontogj'apJiica, vol. xxxix, 

 p. 114). Each of these authors also presents figures of various 

 parts. In the following pages I shall call attention to such 

 features of structure as, in my judgment, are new to science, 

 or which require additional treatment or correction. 



I regard the identification of the parietals as yet uncertain. 

 Professor Cope was himself in doubt regarding them, and 

 thought that perhaps what he called the supraoccipital might 

 really be the coalesced parietals {Cret. Vert., p. 183). Further 



Fig. I. — Skull of Tarpon atlanticiis, seen from right side and partly from below, x \- 



on (p. 188) he concluded that the bones which he at first had 

 identified as the epiotics were the parietals. Crook states that 

 the parietals are completely separated by the large supra- 

 occipital'. He figures them (PI. XVIII) as lying laterad of the 

 epiotics, a situation which appears not probable. The small 

 development of the supraoccipital in the tarpon permits the 

 parietals to meet along their whole median borders, while each 

 epiotic (Fig. i, ep), by its inner anterior angle, comes into 

 contact with the outer posterior angle of the parietal. Should 

 the supraoccipital now be enlarged we might expect the 

 parietals to be reduced posteriorly and more or less separated. 

 It seems to me that in the four rather complete skulls of 

 Xiphactinus before me, two belonging to the United States 

 National Museum, the others my own, I can recognize the 



