GREAT LAKES COREGONIDS 



529 



23, 1917, off Bay City in Saginaw Bay were subsisting almost exclusively on the 

 larvse of the burrowing Mayfly Hexagenia. Sphserium and detritus were present 

 occasionally. 



Coregonus clupeaformis of Lake Superior 



The whitefish of Lake Superior resembles closely, in body form and other char- 

 acters, the whitefish of Lake Michigan. The principal systematic characters that 

 can be expressed numerically are compared below: 



H/S: 



Michigan, (3.2) 3.4-3.7 (4.1). 

 Superior, (3.2) 3.4-3.8 (4.2). 

 Pv/P: 



Michigan, (1.5) 1.7-2 (2.3). 

 Superior, (1.4) 1.6-1.9 (2.3). 

 Av/V: 



Michigan, (1.3) 1.5-1.8 (2). 

 Superior, (1.3) 1.5-1.8 (1.9). 

 L/D: 



Michigan, (3.3) 3.9-4.3 (4.8). 

 Superior, (3) 3.7-4.3 (4.7). 



Gill rakers on the first branchial arch : 



Michigan, (24) 26-28 (30) . 71 



Superior, (25) 26-28 (30)." 

 Lateral-line scales: 



Michigan, (74) 81-88 (93). 



Superior, (77) 81-86 (94). 

 L/H: 



Michigan, (4.2) 4.4-4.8 (5.3). 

 Superior, (4.4) 4.6-4.8 (5). 

 H/E: 



Michigan, (4.4) 4.6-4.9 (5). 

 Superior, (4.1) 4.4-4.7 (5). 

 H/M: 



Michigan, (3) 3.2-3.4 (3.8). 

 Superior, (2.9) 3.2-3.4 (3.8). 



The most important differences that the figures show are a proportionally 

 larger eye for Superior fish, but this character is known to decrease in proportion 

 with growth, and as the Superior specimens average smaller and therefore might be 

 expected to differ in this way from the Michigan fish, the data can not be regarded 

 as establishing differences between the two forms. 



The general appearance in life is essentially silvery, though less so, perhaps, 

 than in most. Leucichthys. The back, as a rule, is pale pea green, palest behind the 

 dorsal, fading toward the tail, and obscured by wide bands of pigment around the 

 free edges of the scales and fins and fine scattered pigment over the entire surface. The 

 color extends on the sides to about the fourth or fifth row of scales above the lateral 

 line and begins then to change to a blue, which is strongest below the line and fades 

 toward the colorless belly. The silvery layer begins to become conspicuous on the 

 ninth row above and reflects on the sides a superficial brassy to purplish iridescence, 

 which is most conspicuous above the lateral line. The top of the head is cartilagin- 

 ous white, frequently with a flesh tone, but it is often so heavily dotted with pigment 

 as to have an almost black cast and to conceal the green patches lying in the cranial 

 cartilages. There is a more or less evident trace of green in the preorbital area. 

 The premaxillaries, maxillary, and mandible also show flesh tones. Otherwise 

 the head is silvery with the reflections of the sides. The fins are whitish, more or 

 less pigmented, sometimes tinted a flesh color at the base, especially the pectorals. 



The color in alcohol is dark, like that recorded for Michigan specimens, except 

 that the specimens from Ontonagon, Mich., the smallest ones in the collection, show 



" Figures for Lake Michigan, except those for gill rakers, lateral-line scales, and H/E are based on an examination of 126 speci- 

 mens ranging in length from 179 to 483 millimeters. The H/E figures are given for 52 specimens between the lengths of 300 and 483 

 millimeters; those for gill rakers for 151 specimens, and those for scales for 191. 



" These and other figures for Lake Superior, except those for H/E are given for 109 specimens ranging in length from 180 

 to 382 millimeters. The H/E figures are given for 55 specimens from 300 to 382 millimeters long. 



