GREAT LAKES COREGONIDS 



545 



rounded, even in individuals in which the premaxillaries are most retrorse. Its 

 lateral surfaces are nearly flat to a line on a level with the superior edge of the maxil- 

 laries and from thence converge sharply in a downward direction, the more sharply 

 as the snout is approached. The dorsal surface of the head is acutely triangular 

 owing to the compression of the entire preorbital and mandibular regions. The 

 width of the head through the nostrils is 17 to 21 per cent of the head length. Its 

 interorbital space is flat or only very faintly convex. A short but heavy median 

 keel runs from a point above the postoculars to a point approximately above the 

 anterior edge of the pupil. A fainter keel originates on each side of it, slightly far- 

 ther craniad, and extends almost to the nares. The ventral surface of the head is 

 likewise acutely triangular in form but is strongly convex from side to side. The 

 branchiostegal membrane, which has 7 or 8 short rays, is trapezoidal in shape. From 

 it the isthmus narrows distinctly to join the mandible. The premaxillaries are more 

 or less retrorse in position, usually making an angle of 100° to 110° with the horizontal 

 axis of the head. The eye is moderate in proportion to the head, contained (3.9) 

 4.3-4.6 (5) times in the head length. Its pupil is oval, so that its cranial angle, 

 usually conspicuous in the coregonids, is rounded off. There are (5) 6-7 (8) +(9) 

 10-11 (12)= (15) 16-18 (19) gill rakers on the first branchial arch. The lateral-line 

 scales run in a nearly straight row and number (84) 87-95 (100). 82 Scale rows 83 

 ^around the body, just in front of the dorsal and ventrals, are (40) 42-45 (46); in front 

 of the adipose and the anus, (31) 33-35 (36); and around the caudal peduncle at its 

 commencement, (24) 25-27 (28). There are usually a few scales conspicuously 

 larger than the rest just behind the occiput. The dorsal rays number 11-12 (13) ; 83 

 anal rays, 9—1 1 ; 83 pectoral rays, 14-16 (17); 83 ventral rays, 10— ll. 83 The length 

 of the pectorals is contained (1.8) 1.9-2.2 (2.3) times in the distance from their 

 origin to that of the ventrals. The length of the ventrals is contained 2.1-2.3 (2.5) 

 times in distance from their origin to the anal. (See fig. 12.) 



The color in life is silvery, as in the other forms, but in the pilot it is less striking 

 on account of the presence of brighter superficial colorations. The entire dorsal 

 surface, including the cranium, is virtually a uniform bronze to sepia brown tinged 

 with green. The exposed surface of the scales of the back, particularly in the pre- 

 dorsal area, is margined with a band of pigment dots, which tend to obscure the 

 coloration. The sides are brownish; the color is strongest above the lateral line, 

 where it is overlaid by silvery with a pinkish cast. The pinkish cast is brightest 

 below the lateral line, but both the pink and the brown beneath it fade as the color- 

 less belly is approached. The sides of the head are also silvery, with a tinge of bronze, 

 which is strongest in the preorbital region, on the dorsal tip of the operculum, and on 

 the iris. The premaxillaries and tip of the mandible are whitish. The maxillary is 

 spotted with fine dots of brown. The basal half of the paired fins and often of the 

 anal is bright salmon pink. The dorsal fin and the basal half of the shortest and 

 three-fourths of the longest rays of the caudal are brown. 



After preservation, all color, including the silvery tone, eventually fades, dis- 

 closing further details of pigmentation. Pigment is evident, then, also on the sides 



82 Sixty-five specimens. 



83 Twelve specimens. 



