728 THE EOCENE FAUNA. 



radii. Caudal fin openly emarginate. Lateral line continuous, uninter- 

 rupted. Two species of the genus are known, both from some beds of 

 possibly tertiary shale which lie on the Laramie beds in Western Dakota. 



Plioplarchus whitei Cope. 



Amer. Jouru. Sci. Arts, 1883, May or June. 

 Plate XXIV g, fig. 1. 



General form elongate oval, the dorsal and ventral outlines of the body 

 about equally convex. The length of the head enters that of the head and 

 body to the extremity of the caudal vertebrae three times, and the depth of 

 the body at the ventral fins enters the same two and two-thirds times. The 

 muzzle is short and obtuse, and the mouth opens obliquely upwards. The 

 orbit is very large, and enters the length of the head to the border of the 

 operculum three times, and is one-third of itself longer than the muzzle. 



The radial formula is: D IX- 12; C. -f 17 + ; A. V - 14 ; V. ?; P. 13. 

 All the soft rays are fissured distally. The dorsal spines increase in length 

 to the last one, as do also the anals. The pectoral rays reach to below the 

 sixth dorsal spine, and beyond the extremity of the ventral fin, which 

 does not quite reach the anal. The soft rays of the anal extend to below 

 the extremity of the vertebral column, forming a well-developed fin. The 

 extremity of the soft dorsal is lost. The external rays of the caudal fin are 

 a little longer than the median. The spine of the ventral fin is not strong. 



The caudal peduncle is moderately nan-ow. The vertebral column is 

 convex upwards anteriorly. Its vertebrae are, caudal XVI; abdominal XII; 

 to the edge of the operculum. A caudal vertebra preserved in place has 

 two lateral fossae, separated by a horizontal keel. The abdominal cavity 

 extends postei'ior to the anterior spinous rays of the anal fin, so that the 

 anterior interhsemals are directed upwards and backwards. The ribs are 

 long. There are four intemeural bones anterior to the dorsal fin. The 

 postcoracoid is elongate. 



There are seven or eight longitudinal rows of scales visible above the ver- 

 tebral column, and sixteen below it, the size diminishing rapidly downwards. 

 All the bones of the head excepting the muzzle and jaws are covered with 



