FISHES OF LAKE SUPERIOR. 269 



Here the membrane is thickened considerably, and continues so on 

 the whole circumference of the upper jaw, following its outlines. 



The mouth is protractile, and when projected outwards carries 

 with it the surrounding membrane. The jaws are Aveak, both max- 

 illary branches of the upper and lower jaw uniting by means of a 

 tendinous membrane. The extremity of the tongue is round, cov- 

 ered with a thick membrane, with a wrinkled surface perforated with 

 small mucous holes. 



A thick layer of mucosity covers the surface of the head. This 

 mucosity is secreted by the crypts of the skin ; these are especially 

 very conspicuous on the space situated between the mouth and the 

 snout, and on the upper side of the latter. They have the appear- 

 ance of irregular meshes excavated in the skin, at the bottom of 

 which we distinguish, by means of a magnifying glass, the crypts 

 which line its surface. 



The body is of a regular form, diminishing insensibly from the 

 anterior side backwards to the dorsal and anal fins, behind which it 

 decreases rapidly towards the tail. This latter goes on tapering, then 

 turns up obliquely, arching itself slightly over the lower lobe of the 

 caudal. The surface of this caudal prolongation is covered with 

 small elongated escutcheons, which become the more slender the 

 more they rise along tlie caudal arch. They begin above the last 

 escutcheon of the lateral row, much resembling the scales of the tail 

 in Lepidosteus. 



The five rows of escutcheons on the sides of the body and along 

 the back are scarcely visible, for they are hidden in the thickness 

 of the body. 



The upper lobe of the caudal fin is composed in its whole extent 

 of spinous rays, generally short and much inclined backwards, di- 

 minishing in length the more they recede, and becoming rudimen- 

 tary at their termination. The lower lobe, which gives to the cau- 

 dal fin its general form, is exclusively composed of articulated and 

 dichotomous rays. Those of the lower margin, much the largest 

 and longest, remain undivided for two-thirds of their length ; they 

 seem even to follow a direction peculiar to /them by a slightly con- 

 cave line. The other rays grow more and more slender the more 

 they rise above the lobe. They bifurcate first in the middle, and 



