No. I.] THE GENUS OF FOSSIL FISHES. 



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p^rietals as wedge-shaped narrow bones which lie between the 

 anterior ends of the pterotics and posterior ends of the frontals 

 on the outside, and the supraoccipital on the median side. I 

 am inclined to believe that the parietals meet along the mid- 

 line in front of the supraoccipital, and really include the 

 elevated surface assigned by Crook to the latter bone, and said 

 by him to be covered with coarse granulations. The posterior 

 pointed end of each bone falls just mesiad of the epiotic. My 

 determination of these bones may be erroneous, but I am 

 wholly unable to find evidences of any suture defining the 

 parietals as located by Dr. Crook. 



The epiotics have been correctly mapped by Dr. Crook. 

 Professor Cope was in doubt about the opisthotics. At first 

 (Cret. Vert., p. 183) he regarded them as forming the postero- 

 lateral angles of the skull ; but, on p. 188, he concludes that 

 these angles are formed by the epiotics, and that the opisthotics 

 are absent. Crook {pp. cit., -p. 115) says that the opisthotics 

 are the largest bones entering into the brain capsule. This I 

 believe to be an error. I am of the opinion that the position 

 and relations of the opisthotics of Xiphactinus are best 

 explained by an examination of the tarpon (Fig. i, op.). Here 

 what may be regarded as the body of the opisthotic is rather 

 small. Its upper end articulates with the pterotic {pt.o), while 

 the greater portion of the body lies against the exoccipital (e.o.). 

 It bends forward, sending a small process to the prootic {pro). 

 From the lower border of the body of the bone there is sent 

 downward and forward to the basioccipital a broad process 

 which is as large as the remainder of the bone. In passing to 

 the lower portion of the basioccipital, this process forms a 

 bridge across a deep and broad fossa which is excavated in the 

 basioccipital, but the roof of which is formed by the exoccipital. 

 Now, the positions and forms of all the other bones in this 

 region are in Xiphactinus almost identical with those of Tar- 

 pon. There are also the same deep cavities in the side walls 

 of the skulls of the two genera. I believe, therefore, that we 

 are justified in concluding that the opisthotic had somewhat 

 similar form, position, and relationships. Moreover, I am con- 

 vinced that this bone is present in three of the skulls at my 



