GREAT LAKES COREGONIDS 



337 



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

 conspicuously smaller than that of those of adjacent rows; gill rakers 15-20, the length of 

 the longesf 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; mandible con- 

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

 contained not less than 1.9 times in the ventral-anal distance Prosopium quadrilaterale 



LAKE MICHIGAN 



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. Maxillaries and premaxillaries usually unpigmented; mandible usually equal to the 

 upper jaw; pectorals usually contained 1.6-1.8 times in the pectoral-ventral dis- 

 tance johannse 



aa. Gill rakers usually more than 32 and less than 45 (except hoyi, which may often have 45) . 

 b. Lower jaw shorter than the upper. 



2. Gill rakers usually 38-42; pectorals usually contained 2-2.2 times in the pectoral- 

 ventral distance; mandible usually immaculate, or at least not conspicuously 

 pigmented; snout and maxillary relatively long, usually contained 3.4-3.7 and 



2.4-2.6 times in the head zenithicus 



3. Gill rakers usually 34-38; pectorals usually contained 2-2.5 times in the pectoral- 

 ventral distance; mandible usually conspicuously pigmented; snout and maxillary 



relatively short, especially in the southern half of the lake reighardi 



bb. Lower jaw seldom shorter than the upper, usually longer. 



c. Maxillary usually immaculate; mandible well developed; fish commonly attaining size 

 of more than 250 millimeters (about 10 inches). 



4. Gill rakers usually 36-43; pectorals usually contained 1.9-2.2 times in the pectoral- 



ventral distance; body shape in side view usually elliptical alpense 



cc. Maxillary seldom immaculate; mandible usually frail; fish seldom longer than 250 

 millimeters (about 10 inches). 



5. Body shape in side view ovate; pectorals usually contained 1.4—1.7 times in the 



pectoral-ventral distance; ventrals usually contained 1-1.3 times in the ventral- 

 anal distance; gill rakers usually less than 41; lateral -line scales usually more than 

 77; fall spawners r kiyi 



6. Body shape in side view elliptical; pectorals usually contained 1.7-2 times in the 



pectoral-ventral distance; ventrals usually contained 1.2-1.4 times in the ventral- 

 anal distance; gill rakers usually more than 40; lateral-line scales usually less than 



78; spring spawners hoyi 



aaa. Gill rakers usually more than 44. 



7. Body shape in side view broadly ovate; flesh fat and soft; pectorals usually contained 



1.6-1.8 times in the pectoral-ventral distance; ventrals usually contained 1.3-1.5 

 times in the ventral-anal distance; maxillary usually contained less than 2.7 times 

 in the head; paired fins usually conspicuously pigmented nigripinnis 



8. Body shape in side view elongately elliptical; flesh firm; pectorals usually contained 



1.9-2.2 times in the pectoral-ventral distance; ventrals usually contained 1.6-1.8 

 times in the ventral-anal distance; maxillary usually contained more than 2.6 



times in the head; paired fins not conspicuously pigmented artedi 



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

 3.1 but less than 3.8 times in the head; mandible usually contained 2.4-2.7 times in the 

 head; gill rakers 24-31; ventrals usually contained less than 2 times in the ventral-anal 

 distance Coregonus clupeaformis 



