46 HAY. [Vol. II. 



The planes of the two surfaces which support the first ray 

 approximately coincide and are directed outward, somewhat 

 backward, and slightly downward, a position different from that 

 given by Cope. 



The first and spine-like ventral ray is constructed like the first 

 pectoral, and may also be compared with that of other Iso- 

 spondyli such as the lake-trout (Cristivomer) and tarpon. Like 

 the first pectoral ray, it seems to have wholly lost its transverse 

 segmentation. These spines, however, show no special physo- 

 clistous characters, as Professor Cope supposed they did. The 

 first ray of my specimen of the ventral fin of X. tJiaiimas is 

 38 mm. wide at the base, and was perhaps originally 60 cm. 

 long ; but this was a very large fish, since its upper jaw had a 

 length of 38 cm. Professor Cope states that the first three 

 rays were spines, and that there were probably no additional 

 rays. However, it seems probable that the rays succeeding 

 the first one were much feebler, were segmented, and longitu- 

 dinally split. There were certainly more than three rays, for, 

 in my specimen, I make out six or eight, and there were prob- 

 ably nine. The second ray has only about one-third the diam- 

 eter of the first, and those following become gradually, probably 

 rapidly, reduced. The inner rays must have been very short, 

 since I find finely split and segmented rays at a distance of 

 only 90 mm. from the base of the rays. In Fig. 10 I have 

 represented the bases of the first and second rays. On the 

 anterior border of the first ray the broader upper half of the 

 ray is seen to project some distance beyond the lower half. It 

 will be noticed, also, that on account of the expansion of the 

 pelvic bone in front of the fin articulation, the fin could not be 

 brought in front of a perpendicular to the body at that point. 



In Cristivomer and Tarpon I find a rudimentary ray in front 

 of, and lying on the base of the first ray. It is short, but has 

 a very long muscular process directed forward and upward. It 

 is more reduced in Tarpon than in Cristivomer. I find no 

 evidence of its presence in Xiphactinus. 



The vertebral column has been described by Professor Cope 

 {Cret. Vert., pp. 188, 193, 195, 199), and briefly by Dr. Crook 

 {i/p. cit., p. 117). I have noted some hitherto undescribed 



