lO Bulletin American Museum of Natia-al History. [Vol. XIX, 



curved saber-like, and the greater part of the front edge is 

 provided with coarse serrations. From the posterior border 

 some rays are probably missing, and a few of those present 

 have been floated away somewhat from the body of the fin. 

 A count of the rays at the base of the fin shows the presence 

 of 45. Even the most posterior of these may be traced to 

 near the anterior border of the fin at the distal end. As in 

 the specimen of P . tenuis, described in this paper, there must 

 have been a posterior fringe of soft flexible rays. 



The breadth of the base of the fin is about 105 mm. Here 

 the rays midway between the two borders are very slender, 

 the exposed edges of four of them occupying only 5 mm.; 

 but they grow broader toward their distal ends, so that the 

 four referred to occupy a breadth of 22 mm. Near the distal 

 ends of those rays which outcrop in the anterior border of the 

 fin, at the middle of its length, we find signs of a separation of 

 each into two portions, as in P . tenuis. In the distal end of 

 the fin the two components are as distinctly separated from 

 each other as they are from the components of contiguous 

 fins. The thickness of the fin at the middle is 9 mm. As in 

 the case of the fin rays of fishes in general, each ray is com- 

 posed of an upper and a lower half. At the base of the fin 

 these become broader perpendicularly to the surface of the 

 fin, so as to form plates. Finally these diverge, so as to re- 

 ceive between them the baseosts. Near the anterior border 

 of the base there is a large acetabular cavity for the reception 

 of the rounded head of the scapula. 



The tooth-like projections on the front of the fin vary in 

 distance apart from 10 to 15 millimeters. Those of the most 

 distal half of the fin protrude beyond their bases as much as 

 5 mm. and are retrorse; those of the proximal half are shorter 

 and are dentate in form. In the proximal half of the an- 

 terior border there is a tooth at the end of each fin ray; in 

 the distal half, a tooth for each of the two subdivisions of the 

 ray. From the tip of each tooth a rounded ridge runs back- 

 ward on the surface of the fin at right angles with the course 

 of the rays. This appears to be for the purpose of strengthen- 

 ing the tooth. Each ridge soon divides into two diverging 



