ADAMS ON THE LAKE TROUTS. 359 



full-grown salmon. The head forms oue-fourth of the total length from 

 the snout to the tip of the caudal. It is rather flat above and convex in 

 profile. Tlie eye is midway between the tip of the snout and the nape, 

 and about twice as near to the former as to the hinder edge of the gill- 

 cover. The labials are fully three times as long as the iutermaxillaries, 

 thus contrasting with the l!famaycush, but identical with the Siscowet. 

 The labial crest does not extend beyond the extremity of the bone, as it 

 does in the Kamaycush. The length of the lower jaw is equal to that of 

 the upper surface of the head. Like other lake and river salmonoids, it 

 has a prominent knob on the extremity of the lower jaw, which in ordi- 

 nary-sized males is not permanent, and only seen during the spawning- 

 season. In old males, however, it is very conspicuous, and, as in the sal- 

 mon, fits into a cavity in the upper jaw ; indeed, it would appear to 

 become developed with age, so that all very large salmonoids have it 

 more or less throughout the year. The gill-covers are almost similar 

 in the three, and broadly- distinctive as compared with the brook-trout 

 and the sea and salmon trouts, while the outline of the gill cover, and 

 the relative dimensions of the operculum, and its points of junction 

 with the suboperculum, in all the American lake - trouts, assimilate 

 closely to the salmon iS. solar, while the crescentic outline of the pre- 

 operculum is broadly distinctive, and resembles that of 8. ferox of 

 Europe. 



In the IS^ew World lake trouts, the pre-operculum bulges to a degree, 

 owing to the enormous development of the great masticating muscle in 

 front. The general features of tlie opercular apparatus in lake-trouts, 

 as compared with other salmonoids, are distinctive. The operculum 

 is four-silled, well rounded, and of greater height than breadth ; the 

 suboperculum is nearly one-third smaller than the last, and is trian- 

 gular in its upper half, elliptical in its lower borders, and terminates at 

 its articulation somewhat in the form of a fish-hook. The operculum, 

 with the exception of the ' Siscowet, is long, slender, crescentic, and 

 almost vertical, with a prominent ridge, and the usual foramina upon 

 its anterior surface. 



The teeth of the Togue are strong, slightly curved, and conical 5 those 

 on the outer and lower maxillaries are the largest. The vomer is armed 

 with a few teeth in a cluster or in regular double row, as is said to be the 

 case in the Namaycush; although in the young of the former the teeth run 

 in a zigzag way down the bone in a single row for some distance, but in 

 old fish there are usually seven. Two adult male Togues examined by 

 me gave the following formula, which it may be remarked is absolutely 

 identical with that given by Eichardsou as the scheme of dentition in 

 the Namaycush, viz: iutermaxillaries, 7-7 ; labials, 19-19; palatines, 

 13-13; lower jaw, 19-19; tongue, 8-8; vomer, 7-7.* 



It is worth}^ of note that in young and adolescent individuals of the 



* Fauna Boreali-Araericana, part third, Fish, p. 182. 



