GREAT LAKES COREGONIDS 



381 



The total number of scale rows around the body just in front of the dorsal and 

 ventrals is, in zenithicus (37) 39-42 (45), with 8 per cent more than 42, and in 

 nigripinnis (40) 41-45 (47), with 51 per cent more than 40. Zenithicus usually shows 

 much less pigment, especially on the tip of the mandible and on the pectorals; the 

 dorsal margin of the pectorals is usually straight, not conspicuously decurved; 

 and the body outline, as seen from the side, is more elliptical than in nigripinnis. 

 In the latter the body is distinctly deepest in front of the dorsal, and the dorsal contour 

 rises sharply from the occiput. The state of development of the sex organs, par- 

 ticularly of the ovaries, is also an aid in separating the species at certain times, as 

 zenithicus spawns in November and nigripinnis in September. 



Zenithicus attains a much greater adult size than Tciyi and hoyi. Small speci- 

 mens may be separated from these two species by their more elongate body shape, 

 less body depth, more elongate head, and included mandible. Small zenithicus are 

 distinguished further from hoyi by their fewer gill rakers on the first branchial arch, 

 which number (32) 36-41 (45), with 17 per' cent more than 40, in small zenithicus, 

 and (37) 41-44 (49), with 83 per cent more than 40, in hoyi. 



Zenithicus may be distinguished readily from artedi by the fewer rakers on the 

 first branchial arch, longer snout, maxillary, head, and paired fins, and the more 

 truncated head as seen from the side. Comparative figures for most of these 

 characters follow. 



Gill rakers on the first branchial arch : 



zenithicus, (32) 39-43 (46), with 4 per cent more than 43. 



artedi, (41) 45-48 (53), with 97 per cent more than 43. 

 L/H: 



zenithicus, (3.6) 3.8-4.1 (4.4), with 2 per cent more than 4.2. 

 artedi, (4.1) 4.3-4.6 (5.1), with 92 per cent more than 4.2. 



H/S: 



zenithicus, (3.1) 3.3-3.6 (4), with 12 per cent more than 3.5. 

 artedi, (3.4) 3.6-3.9 (4.3), with 93 per cent more than 3.5. 

 H/M: 



zenithicus, (2.1) 2.3-2.5 (2.7), with 1 per cent more than 2.6. 

 artedi, (2.5) 2.7-3 (3.1), with 92 per cent more than 2.6. 

 Pv/P: 



zenithicus, (1.3) 1.6-2 (2.4), with 14 per cent more than 1.9. 

 artedi, (1.7) 2-2.2 (2.8), with 84 per cent more than 1.9. 

 Av/V: 



zenithicus, (1) 1.3-1.6 (1.9), with 15 per cent more than 1.5. 

 artedi, (1.3) 1.6-1.8 (2.3), with 91 per cent more than 1.5. 



GEOGRAPHICAL DISTRIBUTION 



My data on the occurrence of zenithicus in Lake Superior are assembled in 

 Table 24 and are platted on the chart in Figure 3. Most of the 32 records are 

 derived from special sets of nets of 2J^ and 2% inch mesh made by me out of 

 various ports of the lake in the course of a survey of the Leucichthys fauna. The 

 records are sufficiently numerous and their sources sufficiently well distributed over 

 the lake to warrant the conclusion that zenithicus occurs all along the shores of 

 Lake Superior where suitable conditions obtain. 



