NEMATOGXATHI. 



63 



Ariina of Giinther's system. In the former case the genus resembles the 

 Phractocephalus or the Piranmtana. In the latter case it will fall into the 

 immediate neighborhood of Arius. These three genera are at present 

 existing in South America, so that it appears that the Nematognatld of the 

 Eocene of the Rocky Mountains present the same neotropical resemblances 

 to be traced in the Dajjedoglossus and Priscacara. 



M}^ expedition obtained remains of four or five species of this genus 

 from the Bridger beds, and one from the Amyzon beds of Colorado; but none 

 have as yet been discovered in the shales of the Green River formation. 



The species are distinguished as follows : 



I. Rhineastes ; a large, massive iiucbal shield. 



Cepbalic o.ssificatiou pappilliforiu B. peltatus. 



II. Astephus; nuchal shield uarrow and short. 



Cephalic ossification in smooth lines; one basiocciijital pit; pectoral 



spines serrate on both edges B. smithii. 



Three basioccipital i)its; pectoral spines serrate on both edges B. calvus. 



Pectoral spiues serrate behind only; curved B.Mrcvatus, 



The cephalic bones of the B. arcuatus are unknown. 

 Rhineastes peltatus Cope. 



Proceedings American Philosophical Society, 1872, 486. 

 Plate V, figs. 1-2. 



Established on cranial and other bones with spines of a siluriform fish 

 of the size of, perhaps, the Amiiinis lopli'ms. The form and the excessive 

 rugosity of the external bony surfaces, reminds one of some of the Brazilian 

 Dorades. The frontal fontanelle is closed, though very distinctly marked 

 by a deep groove, with its fundus smooth. The rugosity consists of innu- 

 merable well distinguished osseous papillae. The cranial ossification is con- 

 tinued posteriori}' as a shield, which is strongl}^ convex from side to side. 

 The spine is symmetrical and probably dorsal. It is compressed and curved 

 antero-posteriorly, and is deeply grooved behind Laterally it is closely 

 striate-grooved; the anterior face is narrowed, obtuse, and minutely serrate, 

 with cross ridges; each side of it is rugose, with several irregular series of 

 pronounced tubercles arranged transversely. 



