ART. II -DESCRIPITONS OF FISHES FROM THE CRETACEOUS 

 AND TERTIARY DEPOSITS WEST OF THE MISSISSIPPI RIVER. 



By E. D. Oo|>e. 



Tri^naspis virgulatus, Oojpe, gen. et sp. nov. 



Character genericus. — Shape anguilliform ; vertebrae elongate, con- 

 tracted medially, famished with wide and short diapophyses over the 

 abdominal region. Cranium elongate, not beaked; jaws furnished with 

 acute teeth of moderate size (but small number in the typical specimen). 

 Dorsal fin short, median in position, its radii cartilaginous. Ventral 

 fins entirely behind dorsal. Caudal and anal fins unknown, the latter 

 probably wanting. The dorsal and ventral surfaces each protected by 

 tripod al shields. Shields of other forms on the sides. 



This, with the genus following, introduces for the first time into the 

 North American extinct fauna the family of the Dercetiform fishes. 

 The relationship of the family has been discussed by various authors, 

 especially by Pictet and Von der Marck. The former regards them as 

 Teleostei; the latter as " Ganoids". As I do not adopt the division sig- 

 nified by the last name, I find Professor Pictet's view nearer to the 

 point. The specimens indicate further that the Bercetidw belong to the 

 Actinopteri, and probably to the order Hemibranchii. The only alterna- 

 tive is the order Isospondyli, and the characters which separate the 

 two are not clearly shown in the specimens. Distinct bones below the 

 pectoral fins may be interclavicles, which belong to the Hemibranchii. 



As compared with the other genera of this family, Tricenaspis differs 

 in the very short dorsal fin and posterior position of the ventrals, with 

 the probable absence of the anal. The scuta differ in form from those 

 of some genera. 



Character specificus. — The head is relatively large and the body slen- 

 der. The fins are all small. The rami of the mandible do not present 

 a long symphysis. The opercula are subround, and the bases of the 

 pectoral fins are quite posterior to them. The dorsal and ventral scuta 

 are triradiate, the median branch of the three being directed anteriorly. 

 A series of smaller triradiate scales extends along the superior lateral 

 region just below the dorsal row, and there is a similar one above the 

 abdominal row on each side. Between these and the vertebral axis 

 there are numerous narrow, band-like scuta, directed backward and 

 toward the vertebrae. Eadii : D. 9 or 10; P. 12 or 13; ventrals disturbed. 

 Vertebrae: to first ray of dorsal fin, 27-28; from dorsal first ray to opposite 



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