FISHES OF LAKE SUPERIOR. 369 



lum the form of a crescent on whose convexity the branchiostegal 

 membrane is continued to the upper margin of the opercukim. 



The branchial fissures are large. There are three strongly devel- 

 oped branchiostegal rays, flattened and arched. The two outer on 

 each side may approach very near to each other on the middle line 

 of the lower surface of the head, where they are parallel for a short 

 distance. The branchiostegal membrane is endowed with great 

 elasticity. 



The rays of the centre of all the fins are bifurcated to the third 

 degree. In front of the dorsal, of the anal and of the ventrals we 

 remark the rudiment of a spinous ray, often very difficult to recog- 

 nize. The following ray is never bifurcated, though distinctly articu- 

 lated as the remaining ones ; this is also the case with the ray of 

 the anterior margin of the pectorals, and mth. the great outer ray 

 of the lobes of the caudal, which for this reason is stouter. 



The anterior margin of the dorsal fin corresponds exactly to the 

 middle of the length of the body, excluding the caudal ; so that it 

 extends behind the most prominent part of the back, along the curve 

 of the posterior half of the body ; its length nearly equals the height 

 of its anterior margin ; its upper margin is very slightly rounded. 

 The anal is both lower and shorter than the dorsal, but its length 

 equals its height. Its outer margin is almost straight. The caudal 

 is admirably regular ; its posterior margin is notched by a subcircu- 

 lar crescent ; the ventrals are oblong, rounded, when extended ; their 

 outer circumference equals three widths of their base ; their poste- 

 rior extremity passes someAvhat beyond the anus. The pectorals 

 have precisely the general form of the ventrals, but they are larger ; 

 their terminal extremity is almost contiguous to the base of insertion 

 of the ventrals. 



Br. 3 ; D. I., 9 ; A. 10 ; C. 3, L, 9, 8, 1., 3 ; V. I., 8 ; P. 14. 



The scales cover more than half of each other by imbrication ; they 

 are oblong in the vertical direction, and seen in their natural posi- 

 tion, they represent lozenges which vary a little according to the 

 regions ; the largest occupy the middle region of the body as far as 

 the pedicle of the tail ; but on this latter region they are broader 

 in proportion to their height. On the back they have almost the 

 size and the form of those of the tail. On the belly they are much 



25 



