268 LAKE SUPERIOR. 



tiguous ; beyond this it dilates, in order to shut the branchial cavity 

 at the lower part of the head, forming a very open curved line ; 

 finally it terminates at a small distance from the mouth. The eyes 

 are at a distance of three and six-eighths inches from the end of the 

 snout. Their form is subcircular, their pupil transversely cleft. 

 Their immediate covering is a smooth membrane, which continues 

 below to the anterior extremity, where it becomes reticulated, but 

 without any appearance of the smallest plate on its surface. At the 

 anterior and upper part of the eye is a small protuberance projecting 

 over the depression in which the nostrils are situated. These latter 

 open at the surface by two orifices on each side. The one of an 

 elliptical form with a free opening, occupies a prominent position, so 

 that it would be observed from both sides of the head, looking at it 

 from above. The other, a larger one, has the form of a crescent, with 

 its convexity turned towards the eye, and placed a little obliquely 

 on the vertical line, extending below the lower line of the eye for 

 two-thirds of its length. 



The lower portion of the head appears as a flat surface rising 

 msensibly from the anterior margin of the mouth to the extremity of 

 the snout. This latter rises gradually in an oblique hne, which begins 

 in front of the barbels. The middle line is convex, the margins are 

 inclined. The barbels, four in number, are situated in pairs on both 

 sides. The two pairs are a little more distant from each other than 

 the two barbels of the right and left side. Their length is nearly 

 the same, of about two inches : their form subconical, growing thinner 

 at their extremity. Behind the barbels we notice a subquadrangular 

 depression in which their base is concealed when they bend back- 

 wards. The mouth is situated on the anterior half of the lower 

 part, in a transversal notch ; it extends from one side of the head 

 to the other, the posterior margin being almost straight, the anterior 

 having an elliptical outline on the middle line. A thick membrane, 

 with a glandular and undulating surface, surrounds the jaws, leav- 

 ing the symphysis of the lower jaw free. Both extremities are 

 attached to the anterior third part of both lower maxillary bones, 

 sending a small membranous expansion towards the symphysis, tak- 

 ing afterwards the direction towards the angles of the mouth. 



