270 LAKE SUPERIOR. 



subsequently several times at a distance which varies for every 

 ray. The lower lobe of the caudal extends not so far backwards as 

 the upper. This latter has the form of a very open arch ; the 

 lower is convex below. The line which joins both extremities is 

 oblique within the upper half; on the middle line it becomes con- 

 cave, giving to the posterior margin of this fin the form of an 

 irregular crescent. 



The dorsal fin is equally notched, forming a crescent on its termi- 

 nal margin. All the rays which compose it are articulated. Those 

 of the anterior margin, four times longer than those of the posterior, 

 are arched backwards, undivided through their whole extent. The 

 other rays dichotomize in the same manner as those of the caudal. 



The anal, longer than broad, is placed opposite and somewhat 

 behind the dorsal. Its form is oblong, the inner and outer margins 

 are rounded ; the posterior margin is straight, bending slightly 

 inwards at the middle. The rays are similar to those of the dorsal. 

 Those of the lower margin being the longest and remaining undivided 

 through the whole extent ; those of the outer margin dichotomize 

 like those of the dorsal. 



The ventral fins, as broad as they are long, are placed half way 

 between the pectorals and the anal. Their posterior margin is almost 

 square, the inner slightly sinuous, the outer rounded. The rays 

 of the former dichotomize from their basis, those of the latter are 

 undivided, like those of the other fins. 



The pectorals are of all fins the most developed. Their greatest 

 length is seven inches and a half, and their breadth nearly four inches. 

 Their form is a rather regular oval, setting aside their margin of inser- 

 tion, which for two-thirds of its extent, from the outer margin, forms 

 a straight line, directing itself obliquely towards the interior of the 

 fin, whilst on the other third we observe a curve which brings the 

 inner margin of the fin back upon itself. The rays of this margin 

 become excessively slender, and remain undivided, like those of the 

 outer margin. Those of the centre dichotomize according to the 

 common rule. 



The number of rays in the fins is as follows : P. 39 to 40 ; D. 34 ; 

 V. 26 ; A. 23. We may count as many as fifty to sixty on the lower 

 lobe of the caudal, but they become indistinct beyond this number. 



