306 LAKE SUPERIOR. 



prominent and covered with very thin scales, which are hidden in 

 the skin. Those covering the opercular apparatus are larger and 

 more conspicuous. The opercular bones are generally smooth ; the 

 preoperculum is rounded ; the operculum is triangular, with its 

 summit turned towards the tail, and terminated by two processes, 

 of which one is a cutaneous, thread-like expansion, the other a direct 

 continuation of the bone. The suboperculum is of an irregular ellipti- 

 cal form, extending along the whole lower margin of the operculum. 

 The interoperculuui is a quite small triangular plate, lost between 

 the bones above named, which constitute the opercular apparatus. 

 The branchiostegal rays, as usual, six in number, are slender and 

 diminish in length on the side of the isthmus between the horns of 

 the hyoid bone. 



The anus is small and a little nearer to the head than to the 

 tail. 



The first dorsal, of a roundish form, is generally separated from the 

 second ; sometimes, however, a small very low membrane unites the 

 hinder margin of the one to the anterior margin of the other. It 

 is composed of nine or ten spinous rays ; the longest occupy the 

 centre of the fin ; they measure nearly five-sixteenths of an inch ; 

 the first has only the half of this height ; the two last, which are still 

 shorter, incline very much on the back. The second dorsal, a little 

 higher than the first, is equilateral, having its upper margin almost 

 straight, and its posterior margin half the height of the anterior mar- 

 gin, where the largest rays are ; they are twelve in number, all bifur- 

 cated, and a few trifurcated. Its insertion measures about half 

 an inch. The caudal is inserted on a slightly dilated pedicle 

 of the tail ; the upper and lower margins, almost straight, diverge 

 a little on their extent ; the posterior margin is truncated almost in 

 a straight line ; there are seventeen rays, divided from the first third 

 part of their length, which is three-eighths of an inch ; on the upper 

 margin we count six, and on the lower five rudiments of rays ; the 

 two following on the two margins remain always below the dimensions 

 of the others, nor do they bifurcate, though they be distinctly 

 articulated transversely. The anal is opposite the second dorsal, 

 it is less elevated, equilateral, but its outer margin is rounded ; the 

 rays, eleven in number, bifurcate beyond their middle ; the ray of 



