1903.] Ha\\ North American Cretaceous Fishes. 25 



ported that the original length was 41 inches. This state- 

 ment is not at all improbable. The second specimen described 

 by Cope (Vert. Cret. Form. West, p. 244F, pi. xliv, fig. 12) is 

 also in the Museum's collection and is numbered 2064. 



The type fin blade has been somewhat distorted by pressure, 

 so that the surface, instead of being flat, as it undoubtedly 

 was originally, is, as Cope says, trough-like. That the sur- 

 face was flat is shown by other specimens in the collection 

 which were obtained for Cope by Sternberg and Hill. The 

 enamelled edge is sharp, sharper than the edge of the regula- 

 tion table knife. The edge is not straight, but has the ap- 

 pearance of having been nicked here and there, as is shown by 

 Cope's figure. This author thought that these irregularities 

 had been produced by the rough uses which the fish had 

 made of the fin; but, since the bottoms of the notches are as 

 sharp as the edge elsewhere, it is not probable that there 

 have been any injuries done to the edge. 



At the base of the fin the anterior rays have been so thor- 

 oughly consolidated that they cannot be counted; but, after 

 making proper allowances, there appear to be about 50 rays 

 entering into the portion of the fin represented by the speci- 

 men. The rays, beyond the most anterior ones at the base, 

 grow wider as they are followed toward the distal end; where, 

 one after the other, they emerge at the anterior border, becom- 

 ing consolidated with those in contact with them. Those 

 which reach the distal half of the fin become divided each 

 into an anterior and a posterior portion, as in the case of P . 

 perniciosa. 



In the case that the fin was originally about 1040 mm. long, 

 that is about 312 mm. longer than it is now, there must have 

 been about 13 more spines entering into its construction, 

 that is 63 altogether; for the last 312 mm. of the length is 

 now occupied by 26 outcropping ends, and these represent 

 13 rays at the base. If this estimate is correct, the fin must 

 have been about 200 mm. wide at the base. 



For the greater part of its length the fin is 20 mm. thick, 

 measured at a distance of 50 mm. behind the edge. Near the 

 base the thickness is still greater. Other specimens in the 



