FISHES OF LAKE SUPERIOR. 287 



shields. On the lower jaw there is a narrow band of teeth, like 

 those of the intermaxillaries. The labials extend a little beyond the 

 intermaxillary to form the angle of the mouth, which corresponds to 

 a vertical line which would pass before the nasal openings. The 

 suborbital bones are very much developed. They are four in number, 

 intimately united, extending from the posterior and lower margin of 

 the eye to the nostrils. The three first, much the smallest, occupy 

 the lower circumference of the orbit ; the fourth, almost as large as 

 the three others together, is the strongest and the most robust and 

 protects the lower margin of the nostrils ; it sends out a prominent 

 point to the space situated between these latter and the eye. 



The opercular apparatus is completely smooth, like the surface of 

 the head itself. The posterior free margins of the bones which com- 

 pose it, are destitute of any kind of spines or denticulation. The 

 most developed, and at the same time the most robust of the bones 

 of this apparatus, is the preoperculum, which occupies almost the 

 whole width of the face. Its form is triangular ; the outer margin of 

 its ascending branch is slightly concave ; the lower branch, the most 

 developed, is straight and encircles the lower margin of the face. 

 The operculum is quadrilateral, its four angles are prominent ; its 

 upper, hinder and lower borders are notched or concave, its anterior 

 margin is almost straight. The suboperculum, small, narrow, 

 oblong, is lodged in the concavity of the lower margin of the opercu- 

 lum. The interoperculum, which is a third longer than the suboper- 

 culum and which it resembles in form, is entirely hidden under the 

 lower branch of the preoperculum. The branchial openings are very 

 large ; they continue to the middle of the lower surface of the head, 

 where they are almost contiguous. The branchiostegal membrane is 

 supported by six curved ra} T s ; the upper ones, which are the largest, 

 are flattened. There are four branchial arches on whose inner border 

 we remark a double row of shields in relief, covered with small card- 

 like teeth, as we observe on the phai'yngeans. 



The disposition of the fins is in striking harmony with the form of 

 the fish. The dorsal, which is the largest, is situated at the middle 

 of the back. Its length equals the height of its anterior margin, 

 being more than twice as high as its hinder margin. The upper 

 margin is straight. There are twelve rays. The two first are short 



