338 



BULLETIN OF THE BUREAU OF FISHERIES 



AA. A single flap between the openings of a nostril; exposed area of the scales of the lateral line 

 conspicuously smaller than that of those of adjacent rows; gill rakers 15-19, the length of 

 the longest not more than 5 per cent of the head; maxillary usually contained more than 

 3.8 times in the head; premaxillaries wider than long, retrorse in position; lower jaw con- 

 tained not less than 2.7 times in the head; no vestigial teeth; body subterete; ventrals usually 

 contained not less than 2 times in the ventral-anal distance Prosopium quadrilaterale 



LAKE HURON 



A. Two flaps between the openings of a nostril; exposed area of the scales of the lateral line not 

 conspicuously smaller than that of those of the adjacent rows; gill rakers more than 23, 

 relatively long and slender; maxillary usually contained less than 3.8 times in the head; 

 vestigial teeth usually present on the premaxillaries, palatines, mandible, and tongue; body 

 usually laterally compressed. 

 B. Premaxillaries longer than wide, usually oblique in position, never retrorse; lower jaw con- 

 tained not more than 2.3 times in the head; gill rakers relatively long and usually numerous; 



maxillary seldom contained more than 3.1 times in the head Genus Leucichthys 



a. Gill rakers usually less than 33. 



1. Length of the pectoral fin usually 1.5-1.8 times in the pectoral-ventral distance; 



pectoral rays usually 17 or 18; jaws usually equal; body shape in side view rather 



ovate; fish spawning in August and September johannse 



aa. Gill rakers 31-45, seldom less than 33 or more than 43. 



b. Body outline in side view ovate; pectorals usually contained 1.4—1.7 times in the pectoral- 

 ventral distance; ventrals usually contained 1-1.2 times in the ventral-anal distance. 



2. Mandible usually projecting and strongly hooked; maxillary pigmented; fish seldom 



over 200 millimeters long (7J*£ inches); usually conspicuously bloated; lateral-line 



scales usually 75-83; gill rakers usually 36-40 kiyi 



bb. Body outline in side view elliptical; pectorals usually contained more than 1.7 times 

 in the pectoral-ventral distance; ventrals usually contained more than 1.2 times in 

 the ventral-anal distance, 

 c. Gill rakers usually 40-43; mandible frail and usually projecting; fish seldom over 200 

 millimeters long (7% inches); snout short; the head in side view sharply triangular; 

 spring spawners. 



3. Maxillary pigmented; fish usually conspicuously bloated hoyi 



cc. Gill rakers usually 33-37; mandible well developed, either longer or shorter; snout 



longer and rounded or truncated, so that the head in side view is not distinctly 

 triangular. Fish attaining adult size of 300 millimeters and more (12^ inches); 

 spawning in fall; pectorals relatively short. 



4. Mandible strong; usually projecting beyond the upper jaw; maxillary usually im- 



maculate; premaxillaries less vertical in position; fish spawning in late Novem- 

 ber alpense 



5. Mandible moderately developed and usually shorter than the upper jaw; maxillary 



usually pigmented; premaxillaries nearly vertical; fish spawning in September- 

 October zenithicus 



aaa. Gill rakers usually more than 43. 



bbb. Body shape in side view ovate; flesh soft and fat; fish seldom found at depths of less 

 than 35 fathoms. 



6. Abdominal fins usually conspicuously black; Pv/P seldom more than 1.8; Av/V 



usually less than 1.5; H/M usually less than 2.7 nigripinnis 



bbbb. Body shape in side view elliptical; flesh firmer and with little oil; fish seldom found as 

 deep as 35 fathoms. 



7. Abdominal fins not conspicuously black; Pv/P usually more than 1.8; Av/V usually 



more than 1.5; L/D usually more than 3.9; H/M usually more than 2.8- .artedi artedi 



8. Abdominal fins usually conspicuously black; Pv/P usually less than 1.8; Av/V usually 

 less than 1.5; L/D usually less than 3.9; H/M usually less than 2.8- -artedi manitoulinus 



BB. Premaxillaries wider than long, retrorse in position; maxillary usually contained more than 

 3.1 times in the head length, but usually less than 3.8; lower jaw usually contained 2.4—2.7 

 times in the head; gill rakers 24-31; Av/V usually less than 1.9 Coregonus clupeaformis 



