GREAT LAKES COREGONIDS 



391 



Gill rakers on the first branchial arch : 



zenithicus, (35) 38-42 (44), with 19 per cent more than 41. 



hoyi, (37) 41-44 (48), with 71 per cent more than 41. 

 Lateral-line scales: 



zenithicus, (70) 75-85 (91), with 73 per cent more than 76. 



hoyi, (60) 67-77 (84), with 11 per cent more than 76. 

 H/E: 



zenithicus, (4) 4.2-4.5 (5), with 74 per cent more than 4.2. 

 hoyi, (3.8) 3.9-4.2 (4.5), with 8 per cent more than 4.2. 



H/S: 



zenithicus, (3.2) 3.4-3.7 (4), with 30 per cent more than 3.6. 

 hoyi, (3.5) 3.7-3.8 (4.1), with 76 per cent more than 3.6. 

 Pv/P: 



zenithicus, (1.7) 2-2.2 (2.6), with 55 per cent more than 2. 

 hoyi, (1.6) 1.8-2 (2.3), with 21 per cent more than 2. 

 Av/V: 



zenithicus, (1.2) 1.4-1.6 (2), with 41 per cent more than 1.5. 

 hoyi, (1.1) 1.3-1.5 (1.7), with 9 per cent more than 1.5. 



Females of the species may be distinguished further by the difference exhibited 

 in the state of development of ova. Zenithicus spawns in November and hoyi in 

 March. 



Zenithicus differs from artedi chiefly in having fewer gill rakers on the first 

 branchial arch, longer ventral fins, head, snout, and maxillary. The figures for 

 these characters for the two species are given below: 



Gill rakers on the first branchial arch : 



zenithicus, (35) 38-42 (44), with 3 per cent more than 43. 



artedi, (41) 46-50 (55), with 97 per cent more than 43. 

 Av/V: 



zenithicus, (1.2) 1.4-1.6 (2), with 12 per cent more than 1.6. 

 artedi, (1.4) 1.6-1.8 (2.3), with 76 per cent more than 1.6. 

 L/H: 



zenithicus, (3.9) 4-4.3 (4.5), with 7 per cent more than 4.3. 

 artedi, (4.1) 4.3-4.5 (5), with 71 per cent more than 4.3. 

 H/M: 



zenithicus, (2.2) 2.4-2.6 (2.8), with 9 per cent more than 2.6. 

 artedi, (2.5) 2.7-3 (3.3), with 91 per cent more than 2.6. 

 H/S: 



zenithicus, (3.2) 3.4-3.7 (4), with 30 per cent more than 3.6. 

 artedi, (3.3) 3.7-4 (4.4), with 84 per cent more than 3.6. 



Zenithicus is less pigmented and paler in color on the back and cranium and on 

 the abdominal fins than artedi; and the mandible, while not much shorter than in the 

 latter, is heavier and less pigmented. Both species spawn at about the same time, 

 so the state of development of the sex organs is of no systematic importance. 



GEOGRAPHICAL DISTRIBUTION 



My data on the occurrence of zenithicus in Lake Michigan are given in Table 28 

 and are platted on the chart in Figure 4. There are 27 records, all but 2 of them made 

 from an examination of the catches of the commercial chub nets set out of 12 ports 

 on the lake. The records show that the species is found along the shores of the lake, 

 except in Green Bay, and in the strip of the Michigan shore between Frankfort and 

 94995—29 7 



