PLECTOSrONDTLI. 749 



Amyzon mentale Cope. 



Proceed. Arner. Philos. Soc, 1872, p. 481. Annual Eeijort, I. c, 1872 (1873), p. 643. 

 Plate LIX, fig. 2, and Plate LX, fig. 2. 



This fish occurs in considerable numbers in the Osino shales, and 

 numerous specimens have been procured. Two only of these are before 

 me at present. They are of nearly similar length, viz, M. .120 and .105. 

 The most elevated portion of the dorsal outline is immediately in front of 

 the dorsal fin. From this point the body contracts regularly to the caudal 

 fin. The dorsal fin is long and elevated in front, and concave in outline, 

 the last rays being quite short. They terminate one-half the length the" 

 fin in front of the caudal fin. The interneural bones are stout in front and 

 weak behind. Dorsal radii III, 26, and (No. 2) (?) II, 23. . 



There are about twenty-three vertebra; between the first interneural 

 spine and the end of the series in the former specimen, in which, also, there 

 are no distinct remains of scales. In the second, scales are preserved, but 

 no trace of the lateral line; there are six or seven longitudinal rows above 

 the vertebral column. 



The anal fin is preserved somewhat damaged; the rays are not very 



long, and number II, 7. The anterior interhsemal is expanded into a keel 



anteriorly. Ventral fins injured. The ribs and supplementaries are well 



developed. The inferior quadrate is a broad bone, with deep emargination 



for the symplectic. Depth No. 2 in front of dorsal fin, M. .025. Length 



basis of dorsal, .026. 



Amyzon commune Cope. 



Bulletin U. S. Geol. Suiv. Terrs., Vol. I, No. 2, p. 50, 1874. 

 Plate V, fig. 21. 



This is the characteristic fish of the Amyzon beds of the South Park 

 of Colorado. In that locality it is the most abundant species. 



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

 enters the length 2.66 times 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. The general form is thus stout 

 and the head short. The front is gently convex, and the mouth terminal. 

 There are fifteen or sixteen rows of scales between the bases of dorsal and 



