GREAT LAKES COREGONIDS 



485 



H/M: 



Av/V: 



Erie, albus, (2.5) 2.7-2.9 (3.3). 



artedi, 2.6-3 (3.3). 

 Michigan, (2.5) 2.7-3 (3.3). 



Erie, albas, (1.4) 1.6-1.8 (2.1). 



artedi, 1.7-2 (2.1). 

 Michigan, (1.4) 1.6-1.8 (2.3). 



H/S: 



L/D: 



Erie, albus, (3.6) 3.8-4 (4.5). 



artedi, 3.6-4 (4.2). 

 Michigan, (3.3) 3.7-4 (4.4). 



Erie, albus, (2.8) 3.3-3.7 (4.3). 



artedi, 3.7-4.8. 

 Michigan, (3.6) 4-4.9 (5.3). 



Pv/P: 



Erie, albus, (1.6) 1.9-2.1 (2.5). 



. artedi, 2.1-2.5. 

 Michigan, (1.6) 1.9-2.2 (2.6). 



The figures show that the Michigan form differs from that of Erie albus most 

 strikingly in having less depth of body. They indicate also that the former has, 

 on the average, more gill rakers on the first branchial arch, more lateral-line scales, 

 and a slightly larger head and eye. The mandible has been found to be longer than 

 the upper jaw in only 8 per cent of the specimens over 225 millimeters in length and 

 usually is equal or shorter. There are very few specimens of the Erie blueback or 

 artedi form for comparison, but the Michigan race seems to be very like it. The only 

 difference seems to be that the Michigan specimens have a larger head and eye and 

 longer paired fins, but these differences may be due to the fact that the Michigan 

 specimens average much smaller. The Michigan race seems, then, to merit the 

 designation artedi. 



The color in life is about like that of the blueback of Lake Erie. There is, as a rule, 

 more pigmentation on Michigan specimens, particularly on the back and head. 

 The ventrals frequently show some pigment, and the anal usually is dotted with 

 black. 



Pearl organs are developed, at least by the males. Specimens taken in Green Bay 

 on November 11, 1920, showed pearls that differ in their development in no material 

 way from that described for the typical form. 



Racial variations. — There is a wide variation in all characters exhibited even by 

 individuals from the same school (see Table 69), but it is likely that, if enough speci- 

 mens were collected, at least the schools from certain areas of the lake would show 

 tendencies to vary in a definite direction. Very few unusual specimens were seen 

 from any part of the lake, and there is, therefore, no reason to believe that any races, 

 sharply differentiated by external characters, such as manitoulinus in Lake Huron, 

 occur in Lake Michigan. The fisherman, however, are of the opinion that two 

 distinct races inhabit Green Bay. The one they catch in the summer at depths of 

 10 to 20 fathoms in gill nets, and the other is caught in fall on the shores in gill nets 

 and pounds. The first mentioned are known as bluefins, in contradistinction to the 

 blue-backed herring, which they are accustomed to take in shallower water. Except 

 that the deep-water fish are paler and perhaps a trifle fatter and of deeper body, 

 characteristics that might easily be induced by the environment, there are no apparent 

 differences, and an examination of some 35 specimens of each supposed variety shows 

 that the two groups do not differ in the systematic characters that ordinarily are variable 



VARIATIONS 



