346 LAKE SUPERIOR. 



sometimes perceived only after removing the investing membrane. 

 The operculum is sub triangular and large, when we consider that the 

 upper and hinder margins pass from one to the other by a curve ; 

 the lower margin is straight and oblique, and as long as the anterior 

 margin is high. The suboperculum is arched on its whole circum- 

 ference, and makes a projection beyond the operculum. The 

 interoperculum, almost completely covered by the preoperculum, 

 presents externally only a small triangular surface, and a small nar- 

 row band below the lower branch of the preoperculum ; though in 

 reality, this bone is as long as the suboperculum, but less broad, having 

 the form of a very acute triangle, of which the summit would be on 

 the anterior side. 



The branchial openings are very ample, and join each other at the 

 lower surface of the head. The branchiostegal membrane, whose office 

 it is to shut this fissure conjointly with the opercular apparatus, is 

 proportionally little developed ; it contains commonly nine, some- 

 times ten very crowded, flattened and almost straight rays. 



The scales are of middle size in proportion to that of the fish. The 

 largest are situated beneath the belly, the smallest under the throat, 

 the thoracic belt and the caudal region. Those of the lateral line 

 are somewhat smaller than those of the adjacent rows. Their form 

 is generally subcircular or irregularly quadrangular, but their verti- 

 cal diameter has a slight tendency to surpass the longitudinal diame- 

 ter. This peculiarity is especially striking on the abdominal region, 

 where really the scales are oblong and of a height sensibly greater 

 than their length ; at the same time that their outlines become more 

 regular and nearly oval. Their imbrication has even here some- 

 thing peculiar in being less close ; the rows appear independent, and 

 give to the fish a barred aspect. The outlines of those of the late- 

 ral line are the most irregular. The outer margin is in all more or 

 less circular and entire. The lateral line itself is nearly straight and 

 nearer to the back than to the belly ; it begins from the upper angle 

 of the operculum and extends itself to the middle of the caudal. 



The anterior margin of the dorsal fin corresponds to the middle of 

 the space contained between the extremity of the snout and the basis of 

 the caudal ; the fourth and fifth rays are the longest ; the first two 

 short and rudimentary spines are applied against the third, which is 



