FISHES OF LAKE SUPERIOR. §41 



margins ; their posterior extremity not attaining a vertical line whicli 

 would descend through the centre of the eyeball. The mandibles, 

 situated on the inner margin of the maxillaries, are small and narrow, 

 with an undulated outhne terminated above by a slender and acute 

 process. The suborbitaries cover two-thirds of the face. 



The preoperculum is concave on the middle of its ascending 

 branch ; its posterior angle is rounded, and extended to the loM'er 

 margin of the face, and, conjointly with the lower branch, nearly 

 covers entirely the prolongation of the interoperculum towards the 

 lower maxillary. The part of the interoperculum which remains un- 

 covered, is triangular ; the upper angle rises before the operculum. 

 This latter is higher than it is broad above, straight or slightly con- 

 cave,^ rounded behind, oblique and straight on the suboperculum, 

 which is the most regular of the bones of this apparatus, being arched 

 on its lower edge, and somewhat more narrow behind than before. 



The branchial fissures continue beneath the head, the branchioste- 

 gal membrane of the right side unites to that of the left on the region 

 of the isthmus, where they are contiguous, the first jointed beneath 

 the second. The branchiostegal rays, eight in number, are very 

 close, flattened, and almost straight. 



The scales are proportionall}'^ large, of subcircular form, the inner 

 margin irregular and angular. The largest occupy the middle of 

 the trunk and the abdominal region, where they measure more than 

 a quarter of an inch ; they diminish towards the thoracic arch, the 

 back and the tail, where they are smallest. On the middle Une of 

 the belly their form is much elongated and elliptical. Their termi- 

 nation is very remarkable on the basis of the caudal, resembling 

 somewhat the fork of this fin by the concave fine they form. The 

 lateral line is near the middle, rather near to the back, and is slightly 

 inflected on the abdomen by a very protracted curve. 



The dorsal fin, situated on the middle of the back, is much higher 

 than it is long, and its margins are straight ; its first ray is short 

 and simple ; the second does not reach beyond two-thirds of the 

 height ; it is articulated, but not bifurcated. The adipose fin is long 

 and narrow. The anal, longer and less high than the dorsal, is con- 

 cave on its terminal margin ; it somewhat exceeds the adipose fin 

 backwards ; its height somewhat exceeds its length. The caudal is 



