ISOSPONDYLI. 75 



the inferior median line are large and acute. The scales are rather small, 

 and are delicately grooved ; twenty rows may be counted between the 

 vertebral column and the dorsal fin. 



Measurements. 



Total length 365 



Length of head 083 



Length (axial) to below first dorsal ray 145 



Length to above first anal ray . 185 



Length to base of external caudal rays 285 



Depth at orbit 055 



Depth at occiput 093 



Depth at first dorsal ray 118 



Depth at middle anal ray 050 



Depth at base of caudal fin 030 



Not rare at Twin Creek ; specimens occur of fifty centimeters length, 

 or about the size of the shad. 



DiPLOMYSTUS ANALIS Cope. 



Bulletin U. S. Geol. Surv. Terrs., 1877, p. 809. 

 Plate VII, fig. 4; Pl.ate VUI, fig. 3; Plate X, fig. 2. 



Radial formula: D. I. 11; A. I. 40. Vertebrae: dorsal, 17-18; caudal, 

 23-24. This species is more elongate in proportion to its depth than either 

 of the other species, the length being three times the greatest depth. The 

 anal portion of the body is considerably longer than the abdomen, and the 

 anal fin is long and with short rays. The ventral fin commences well in 

 front of the dorsal, whose last ray is considerably in advance of the first 

 anal ray. The pectoral fin reaches the ventral, and contains thirteen rays. 

 The greatest depth is at the pectoral region, the outlines contracting to the 

 base of the anal fin. The dorsal outline is convex. The profile descends 

 gently. The muzzle is half as long as the diameter of the orbit, which 

 enters the length of the head three times. The latter enters the length 

 without the caudal fin three and three-fourths times There is a row of 

 short, conical teeth along the middle line of the mouth, which is not on the 

 vomer, but is on the parasphenoid or axial hyal bones. Similar teeth exist 

 in the mouth of I), dentatus. The jaws may be furnished with minute teeth, 

 or they may be wanting. The scales are thin and difficult to count ; there 

 are fifteen rows between the vertebral column and the anterior anal rays. 



