1903.] ^'^y'l -North American Cretaceous Fishes. 89 



satisfactory specimens of those described by Cope, and for 

 other species which may be 3'et unknown. That fishes are 

 abundant in the soft Hmestone whence Dr. Hayden obtained 

 his specimens, is shown by Plate V, which reveals three types 

 on one side of a block, while a fourth type is found on the 

 other side, besides a part of a large undescribed fish. 



The figures of the species furnished on the plates are of the 

 natural size and may be of some value in identifying other 

 specimens, but they are difficult subjects to illustrate. 



DERCETID^. 



Triaenaspis Cope. 



This genus was established by Cope in the ' Bulletin of 

 the U. S. Geological and Geographical Survey of the Terri- 

 tories,' Volume IV, 1878, page 67. The type is T. virgulatus 

 Cope. Dr. A. Smith Woodward unites the genus with Lepto- 

 trachelus, but the present writer is inclined, for the present, 

 to regard it as distinct on account of the backward position 

 of the ventral fins and the relatively short head. The type of 

 the genus LeptotracJ veins, L. armatus, possesses a dorsal fin of 

 apparently about 12 rays, with the ventrals beneath the front 

 of this dorsal. In Tricenaspis the dorsal is still shorter, not 

 having beyond 10 rays, and the ventrals are placed a dis- 

 tance behind the origin of the dorsal equal to one-third of 

 the distance from the head to the dorsal. 



Triaenaspis virgulatus Cope. 

 Plate V, Fig. i. 



TricBnaspis virgulatus Cope (E. D.), Bull. U. S. Geol. and Geog. Surv. 



Terrs. IV, 1878, p. 67. — Hay (O. P.), Bibliog. and Cat. Foss. 



Vert. N. A. 1902, p. 397. 

 Leptotrachelus virgulatus Woodward (A. S.), Cat. Foss. Fishes, IV, 



1901, p. 187. 



Of this species Professor Cope possessed, so far as can be 

 determined, only the specimen here figured (PI. V, Fig. i) 

 and a fragment of another. The present number of the type 



