GREAT LAKES COREGONIDS 



395 



torals and anal, and the ventrals are usually immaculate. The maxillary is also 

 sometimes unpigmented. 



Males taken on the breeding grounds off Cheboygan and Rogers, Mich., during 

 the last half of September and the first half of October show pearl organs, which 

 are distributed on the scales as in the Lake Michigan specimens and differ from them 

 in their development only in being smaller. It is possible, however, that the indi- 

 viduals examined have not attained their full nuptial dress. 



VARIATIONS 



Virtually all specimens of the species obtained have come from the same locality 

 so that there are no data on local variation. Small individuals, however, differ in 

 certain respects from large ones. In Table 31, 10 specimens of less than 200 milli- 

 meters and 10 specimens larger are compared extensively, and in Tables 8 to 11 are 

 given the variations of some of the principal characters for all collected specimens 

 of either class. A resume is given below: 



H/S: 



Large specimens, (3.2) 3.4-3.7 (4). 

 Small specimens, (3.2) 3.5-3.8 (4.3). 

 Pv/P: 



Large specimens, (1.6) 1.9-2.1 (2.3). 

 Small specimens, (1.7) 2-2.2 (2.6). 

 Av/V: 



Large specimens, (1.2) 1.5-1.6 (1.8). 

 Small specimens, (1.1) 1.3-1.6 (1.7). 



Gill rakers on the first branchial arch: 



Isarge specimens, (34) 37-40 (44). 



Small specimens, (32) 35-38 (41). 

 L/H: 



Large specimens, (3.9) 4.1-4.3 (4.5). 

 Small specimens, (3.7) 4-4.2 (4.4). 

 H/E: 



Large specimens, (3.9) 4.2-4.6 (5.2). 

 Small specimens, (3.5) 3.7-4.1 (4.3). 

 H/M: 



Large specimens, (2.3) 2.4-2.6 (2.7). 

 SmaU specimens, (2.2) 2.5-2.7 (2.9). 



The data indicate that smaller individuals have fewer gill rakers, a somewhat 

 longer head, a larger eye, a somewhat shorter snout, maxillary, and pectorals, but 

 somewhat longer ventrals. The small fish, however, are chiefly from a locality 

 different from that which yielded the larger ones and may belong to another race. 

 The body depth is also less, of course. 



The smallest collected specimens (139 millimeters) were sexually mature, but 

 some immature individuals were found as long as 215 millimeters. 



COMPARISONS 



ZenitMcus resembles most closely alpense. A discussion of the differences between 

 these two species may be found on page 371. ZenitMcus is compared with johannse 

 on page 357. 



ZenitMcus is distinguished from nigripinnis by its paler fins (which in nigripinnis 

 are often very black), more fusiform and shallower body, more elongate and narrower 

 head, more included mandible, and by the fewer gill rakers, which number (34) 

 37-40 (44), 48 with 2 per cent more than 41, as compared with (40) 46-50 (52), with 

 97 per cent more than 41 in nigripinnis. Females of the two species can be dis- 

 tinguished, likewise, by the degree of development of their ova, for zenitMcus spawns 

 prior to the middle of October and nigripinnis after November. 



18 Figures in this paragraph are given for specimens 200 millimeters or more in length. 



