EEPOKT ON ICHTHYOLOGY. 403 



The radial formula is as follows: 



D. VIII. 17; A. 13; P. 15; V. I. 4. 



The lateral line, from the scapular bones to the endof the second dorsal I'm, is well 

 marked; it is then deflected and very obscure. 



The color is grayish anteriorly and brownish posteriorly. It is covered with black 

 spots, which, on the head and anterior portion of the body, are very small and numer- 

 ous, but posteriorly are larger, confluent, and much fewer. The dorsal, caudal, and 

 pectoral fins are quite thickly spotted on the rays; the rays of the anal have also a 

 few spots. The ventrals are nearly immaculate. 



This species is perhaps almost the only smooth American Franeidid which can 

 be at once readily distinguished. A single specimen was obtained by Pr. (ieorge 

 Suckley, in the summer of 1859, between Bridgets Pass ami Fort Bridger. It is 

 four inches in length. 



POTAMOCOTTUS CAEOLIXJO, Gill. 



By its general form, this species belongs to the group of which the Potatnocotius 

 Ricliardsonii is the type, and is nearly allied to that species. 



The body is elongated, slender, and compressed. 'Hie head forms twenty-cighl 

 hundredths of the total length, and the caudal eighteen hundredths. The trunk is 

 anteriorly subcylindrical, and its height equals the length of the caudal tin. The 

 thickness at the base of the pectorals is as great or slightly greater than the height. 

 From the region of greatest height, the body regularly declines to the caudal peduncle, 

 whose height equals a third of the greatest, The breadth declines still more rapidly: 

 at the anus, it is equal to little more than half of that at the base of the pectorals, or to 

 a tenth of the total length. 



The head is oval and depressed above. From the snout to the membranous oper- 

 cular margin, it forms twenty-eight hundredths of the total length: its breadth is about 

 a sixth less than the length. The profile, from the dorsal fin to the snout, is scarcely 

 convex. 



The mouth is large; the jaws arched and receding; tlie distance between the 

 extremities of the mamillaries exceeds a sixth of the entire length, and nearly equals 

 the length of the caudal fin. The maxillaries terminate under the posterior margin ot 

 the pupil. The upper jaw extends beyond the lower. 



The jaws are armed with acute, curved, approximate teeth; the band on the inter- 

 maxillaries is almost entire, and extends with little diminution of width to the extrem- 

 ities of those bones. The band on the lower jaw is separated by a symphysial inter- 

 val; it diminishes in width to the corners of the mouth. The vomerine and palatine 

 bands are well developed, and about as large as that of the lower jaw. 



The eyes are moderate, the longitudinal diameter of the orbit equaling a sixth ot 

 the head's greatest length. The distance between the center of the pupil and the snout 

 equals a tenth of the entire length. The interorbital space is scarcely as great as the 

 diameter of the orbit. 



The preopercular spine is large, and curved upward; the two inferior are tuber- 

 cular, the last one smallest. The subopercular spine is acute, and points obliquely 

 forward and downward. 



