GREAT LAKES COREGONIDS 



351 



VARIATIONS 



Racial variations. — Specimens collected from no area in the lake show distinctive 

 characteristics, and there are not enough specimens in my collection to show whether 

 there are races distinguished by average differences in systematic characters. 



Size variations. — Only two specimens smaller than 200 millimeters have been seen. 

 These measured 181 and 190 millimeters. There was one of each sex, and both were 

 sexually mature. 



comparisons 10 



Johannx resembles most closely alpenx. It is distinguished from this species 

 principally in having a less elliptical body outline as seen from the side, a more 

 elongated and pointed head, fewer gill rakers on the first branchial arch, longer 

 paired fins, and more lateral-line scales. It has also, on the average, a larger head, 

 a shorter mandible, and spawns about three months earlier, so that at certain seasons, 

 at least, the state of ripeness of the sex products will serve as a distinguishing char- 

 acter to separate the two species. The comparative figures for some of the above- 

 mentioned characters follow: 



Gill rakers: 



johannx, (26) 27-32 (36). 



alpenx, (33) 36-43 (46), with 86 per cent more than 36. 

 Lateral-line scales: 



johannx, (74) 80-90 (95), with 35 per cent more than 85. m 

 alpense, (71) 78-85 (96), with 10 per cent more than 85. 

 Pv/P: 



johannx, (1.5) 1.6-1.8 (2.1), with 16 per cent more than 1.8. 

 alpenx, (1.6) 1.9-2.2 (2.5), with 89 per cent more than 1.8. 

 Av/V: 



johannx, (1.1) 1.2-1.5 (1.6), with 6 per cent more than 1.5. 

 alpenx, (1.2) 1.4-1.7 (1.9), with 54 per cent more than 1.5. 



Johannx is distinguished from zenithicus principally in the number of gill rakers 

 on the first branchial arch, in the pigmentation of the premaxillaries and maxillary, 

 in the length of the paired fins and mandible, and in body shape. Johannx always 

 has less than 37 gill rakers on the first branchial arch; zenithicus has more than 34. 

 The premaxillaries and maxillary, particularly the maxillary, usually are immaculate 

 in johannx and pigmented in zenithicus. The value for Pv/P for johannx is (1.5) 

 1.6-1.8 (2.1), with 16 per cent more than 1.8; for zenithicus (1.7) 2-2.2 (2.6), with 89 

 per cent more than 1.8. The mandible also is shorter than the upper jaw, and the 

 slope of the body contours, as seen from the side, is more gradual in zenithicus. The 

 state of development of the ova in the ovaries, also often will serve to separate 

 females, inasmuch as johannx spawns in August and September and zenithicus in 

 November. 



Johannx is distinguished from reighardi principally by the body shape, which in 

 reighardi is much more terete; by the fewer gill rakers on the first branchial arch, 

 longer paired fins, and longer mandible, snout, and maxillary. Johannx also has, 

 on the average, more lateral-line scales, a proportionally larger head and smaller 



10 Figures given in this section for proportions are based on specimens 200 millimeters or more in length, except for artedi, where 

 the limit is 225 millimeters. Counts are given for specimens of all sizes. 



