GREAT LAKES COREGONIDS 



357 



that the only differences recognizable in the two classes are differences of proportion. 

 The head, expressed in terms of body length, is relatively though but slightly larger 

 in smaller specimens. The most striking difference is shown in the ratio that exists 

 between the measurements of the head and eye in the two groups. The complete 

 data in Table 9 show that for the smaller specimens the eye is contained (3.6) 4-4.3 

 (4.5) times in the head length, while for the larger specimens the proportion is (3.9) 

 4.3-4.8 (5.3). The relation between the length of the head and its other parts appears 

 to remain unchanged by growth. The pectoral and anal fins show a decrease in 

 relative length with increased size. The larger fish are relatively deeper. 



Most individuals that have attained a length of 195 millimeters have been 

 found to be sexually mature. No mature specimens have been seen smaller than 

 165 millimeters. Maturity probably is determined by age rather than by the size of 

 the specimen. 



COMPARiSONS 18 



Johannse may be mistaken most frequently for alpense, though small specimens 

 might be confused with bloaters or kiyis. Johannse has fewer gill rakers on the first 

 branchial arch, longer paired fins, more pectoral rays, a shorter and less-developed 

 mandible, a less fusiform body shape (as seen from the side), and its head is more 

 acutely triangular in side view. The chub spawns in September, while the longj aw 

 spawns in November, so that the state of development of the sex organs often may 

 serve to separate the two forms. The longj aw attains a greater size. A comparison 

 of certain characters of the two species follows: 



Gill rakers on the first branchial arch: 



johannse, (25) 27-31 (35), with 7 per cent more than 31. 



alpense, (31) 34-40 (44), with 99 per cent more than 31. 

 Pv/P: 



johannse, (1.3) 1.5-1.8 (2.1), with 23 per cent more than 1.7. 

 alpense, (1.6) 1.8-2.1 (2.3), with 89 per cent more than 1.7. 

 Av/V: 



johannse, (1) 1.2-1.4 (1.6), with 9 per cent more than 1.4. 

 alpense, (1.3) 1.4-1.7 (1.9), with 72 per cent more than 1.4. 

 Pectoral rays: 



johannse, (15) 17-18 (19), with 43 per cent more than 17. 

 alpense, (14) 15-17 (18), with 3 per cent more than 17. 



Johannse differs from zeniihicus in respect to length of mandible, which in the 

 former usually is equal to the upper jaw and in the latter shorter; in the pigmentation 

 of the maxillary, which is usually immaculate in the former and pigmented in the 

 latter; in the shape of the body, which in side view is less elliptical in the former; 

 in the fewer gill rakers on the first branchial arch; and in the longer head and paired 

 fins. Johannse also has, on the average, a longer snout and more pectoral rays and 

 spawns about a month earlier. A numerical expression of the more significant 

 characters follows: 



Gill rakers: 



johannse, (25) 27-31 (35). 



zeniihicus, (34) 37-40 (44), with 89 per cent more than 35. 



11 Figures for proportions in this section are given for specimens 200 millimeters or more in length, except those for artedi, 

 where the limit is 225 millimeters, and for kiyi and the specimens of johannse compared with it, all of which are under 200 milli- 

 meters long. Counts are given for specimens of all sizes. 



