748 THE AMYZON BEDS. 



Measurements. 



M. 



Length of head to clavicle (below) O.Ol'^O 



Width of head (below) 0360 



Width of scapular arch (below) 0110 



Expanse of modified diapophysis — • 0200 



Length of modified vertebrjB - 0115 



Length of pectoral spine 0210 



From the Tertiary shale of the South Park, Colorado. 



PLECTOSPONDYLI. 

 AMYZON Cope. 



Proceed. Amer. Philos. Soc, 1872, p. 480. Annual Report U. S. Geol. Surv. Terrs., 1872 (1873), p. 642. 



Allied to BuhalicMhys. An open frontoparietal fontanelle; the pre- 

 maxillary forms the entire superior arch of the mouth; the pharyngeal 

 bones are expanded behind; there are twelve to thirteen rays of the ventral 

 fin; there is a lateral line of pores which divides the scales, piercing their 

 margin. 



Dorsal fin elongate, with a few fulcral spines in front, and the anterior 

 jointed rays osseous for a considerable part of the length. A few short 

 osseous rays at front of anal fin. Scales cycloid. Caudal fin emarginate. 

 Mouth rather large, terminal. 



The characters of this genus are those of the Catostomidce. There are 

 three broad branchiostegals. The vertebrae are short, and the haemal spines 

 for the caudal fin are distinct and lather narrow. In one specimen a 

 pharyngeal bone is completely preserved. It is slender, and with elongate 

 inferior limb. The teeth are arranged comb-Hke, are truncate, and number 

 about thirty to forty. The dentary bone is slender and toothless, and the 

 angular is distinct. The premaxillary appears to extend beneath the whole 

 length of the maxillary. Should this feature be substantiated, it will indi- 

 cate a resemblance to Cyjirinidce. The maxillary has a high expansion of 

 its superior margin, and then contracts towards its extremity. Above it 

 two bones descend steeply from above, which may be out of position. The 

 preoperculum is not serrate. The superior ribs are well developed. This 

 form approaches in its anterior mouth, the true Cyprinidce, through Buhalich- 

 tliys. It Avas the first extinct form of Catostomidce found in this country. 

 Species more nearly allied to the existing ones are found in the Pliocene 

 beds of Oregon and Idaho. 



