1 6 Bulletin American Museum of Natural History. [Vol. XIX, 



in the latter species, the base of the fin is undulated for a few 

 centimeters, but beyond this the character of the edge in the 

 two species is very different. In P. tennis the undulations 

 subside and the edge is continuous; in P. perniciosa, the 

 elevations increase in height and soon take the form of hooked 

 teeth. 



No. 1620 of this Museum, a part of the Cope Collection, 

 probably belongs to this species. It appears to differ only 

 in having the edge resemble a series of waves whose summits 

 are not rounded but sharp (like Figs, i, 2, PI. Ixiii, of Stewart's 

 memoir) and in having them continued well out toward the 

 distal end of the fin. Such fins possibly belong to a distinct 

 species. This specimen displays the distal end of the fin 

 apparently to within a few centimeters of the tip (PI. I, 

 Fig. 3). Behind the rays which are consolidated to- 

 gether are several others which evidently have been only 

 loosely connected and which have been subdivided into very 

 fine filaments. Evidently, too, the hindermost of these loose 

 rays did not reach quite to the tip of the fin. It is quite 

 probable, therefore, that a considerable number of soft flexi- 

 ble rays occupied the hinder border of these remarkable fins. 

 No cross-segmentation of these rays can be observed. As 

 stated under P. perniciosa, there is some reason to doubt 

 that P. tenuis is distinct from the species just mentioned. 



Protosphyraena dimidiata {Cope). 



Erisichthe nitida Cope (E. D.), Bull. U. S. Geol. and Geog. Surv. Terrs. 

 Ill, 1877, p. 822. 



Protosphyrcsna nitida Loomis (F. B.), Palaeontogr. XLVI, 1900, p. 

 227 (in part), pi. xix, figs. 6, 7. 



Erisichthe dimidiata Cope (E. D.), Proc. Amer. Assoc. Adv. Sci. XXVI, 

 1878, p. 300. 



Protosphyrcsna dimidiata Hay (O. P.), Bibliog. and Cat. Foss. Vert. 

 N. A. 1902, p. 379. 



This species, the type of which is now in the American 

 Museum of Natural History, having the number 1635, was 

 originally described as belonging to Erisichthe nitida. How- 

 ever, within the next year, Prof. Cope came to the conclusion 



