54 MONOGRAPH OF THE FRESH WATER III. 



much less obtuse, and the mouth more deeply cleft. The eyes are subcircular : 

 their longitudinal diameter is contained four times in the length of the head. The 

 interorbi to-frontal space is equal to the half of that diameter. The anterior 

 nostrils are situated midway between the orbit and the extremity of the jaws; the 

 posterior ones are nearer the orbits. 



The preopercular spine is hook-like, very acute, and different in all respects 

 from that of C. viacosus. It resembles more that of C. Bairdii than any other 

 species. The subopercular spine is slender and very acute. 



In spite of the great resemblance between the fins of this species and the pre- 

 ceding one, a careful comparison shows that the paired fins are proportionally 

 shorter. The base of the pectorals is slightly crescent shape ; the tip of its rays 

 scarcely reach the anterior edge of the second dorsal fin. The five uppermost rays 

 do not overrun their membrane quite as much as exhibited in the figure. The 

 ventrals are nearer the isthmus than in C. viscosus, and when bent backwards, they 

 leave a greater space between their tip and the vent. Their insertion takes place 

 immediately under the base of the pectorals instead of being situated behind. 



The first dorsal is nearly of the same height with the second; it is longer than 

 in C. viscomis ; its upper edge is also more convex. There are eight slender rays, 

 the first and last being of equal size. The second dorsal is contiguous to the first, 

 and terminates at a greater distance from the base of the caudal than in ('. riscosus. 

 It contains seventeen rays, or only sixteen, the last one, double. The caudal fin is 

 posteriorly truncated, whilst it is rounded in C. viscosw. It forms nearly the sixth 

 part of the total length. The origin of the anal is under the fourth ray of the 

 second dorsal, and terminates under the thirteenth. When bent backwards the 

 tips of the rays do not reach as far as those of the second dorsal. 



Br. 6. D vill. 17. A 12. C 1. I. 5. 4. I. l. V I. 3. P 14. 



All the rays are unbranched with the exception of two in the centre of the 

 caudal, which, however, bifurcate only once beyond the middle of their length. 



The vent is situated nearer the base of the caudal fin than the tip of the snout. 



The lateral line follows the curve of the back ; it vanishes already under the 

 sixth ray of the second dorsal, whence the series of minute pores is very little con- 

 spicuous-. Its fall near the tail takes place less abruptly than in C. rincosus. 



This species inhabits the southern and eastern shores of Lake Superior, where it 

 has been collected first by Prof. James Hall of Albany, and afterwards by Prof. 

 Agassiz, in whose cabinet specimens arc still preserved. It is also to be seen in the 

 collection of fishes at the Smithsonian Institution. 



The specimen fitrmvd is tin- laivst we have seen. Its total length is tlnvr 

 inches and one-sixteenth. 



