50 



AMYZON, Cope, 



Hayden's Annual Eeport, 1872, 642. 



Amyzon commune, s2). nov. 



In describing this species, the following additions to our knowledge 

 of the generic characters may be made. There is an open fronto-parie- 

 tal fontanelle ; the premaxillary forms the entire superior arch of the 

 mouth; the pharyngeal bones are expanded behind ; there are 12 to 13 

 rays of the ventral fin; there is a lateral line of pores, which divides 

 the scales it pierces to the margin. 



The greatest depth of the body is just anterior to the dorsal flik, and 

 enters the length "^.GQ times to the base of the caudal fin, or a little 

 more than three times, including the caudal fin. The length of the head 

 enters the former distance a little over 3.25 times. Tbe general form is 

 thus stout and the head short ; the front is gently cofivex, and the mouth 

 terminal. There are fifteen or sixteen rows of scales between the bases 

 of the dorsal and ventral fins. They are marked by close concentric 

 lines, which are interrupted by the radii^of which eight to fifteen cross 

 them on the exposed surface, forming an elegant pattern. At the cen- 

 ter of the scale the inturrupted lines inclose an areolation. The ex- 

 tended pectoral fin reaches the ventral or nearly so; the latter origi- 

 nates beneath the anterior rays of the dorsal, or in some specimens a 

 little behind that point. They do not reach the anal when appressed. 

 The anal is rather short, and has long anterior radii. The dorsal is ele- 

 vated in front, the first ray being a little nearer the basis of the caudal 

 fin than the end of the muzzle. Its median and posterior rays are much 

 shortened ; the latter are continued to near the base of the anal fin. 

 Eadii, D. 33; P. 14 ; V. 13; A. 12. The caudal is strongly emarginate 

 and displays equal lobes. 



Measurements. 



M. 



Length of a large specimen (10.25 inches) 0.250 



Length of a medium specimen 182 



Depth at occiput 043 



Depth at dorsal fin 057 



Depth at caudal peduncle 023 



Length of head, axial 044 



Length to D. 1, axial 075 



Length to end of dorsal, axial ■ 131 



Length to basis of caudal fin 146 



Length of basis of anal fin 023 



There are 38 or 39 vertebrae, of which 9 are anterior to the first inter- 

 neural spine, and 14 between that point and the first caudal vertebra. 



A very large number of specimens was obtained by Dr. Hayden and 

 myself from the Tertiary shales of the Middle and South Parks, Colo- 

 rado. , They display but insignificant variations in all respects, and fur- 

 nish a good basis of determination. They all differ from the A. mentale 

 (Cope, Proceed. Amer. Philos. Soc, 1872, 481) in the larger numbers 

 of vertebrae and dorsal and anal fin radii, and greater prolongation of 

 the dorsal fin. It is, however, nearly allied to the species of the Osino 

 shales. The only fish found associated with this one is the small nema- 

 tognath just described. The predominance of these types and exclusion 

 of the brackish-water genera Asineops, Erismatopterus^ and Cliipea, so 

 abundant in the shales of the Green River epoch, indicate a more lacus- 

 trine, and hence, perhaps, though not necessarily, later deposit. 



