GREAT LAKES COREGONIDS 



371 



4.5-4.9 (5.2). The maxillary likewise appears to decrease slightly in relative size, 

 and the ventral fin becomes relatively shorter with increased growth. The values 

 forH/M are (2.3) 2.4-2.6 (2.7) and (2.3) 2.5-2.6 (2.8) and for Av/V are (1.1) 1.3-1.5 

 (1.7) and (1.3) 1.4-1.7 (1.9) for small and large fish, respectively. The depth and 

 width, of course, become greater as the individual approaches maturity. 



Specimens of both sexes 160 millimeters long appear regularly to be approaching 

 sexual maturity. Fish as small even as 145 millimeters have exhibited maturing 

 sex glands. 



COMPARISONS 



Alpense resembles closely only johannse and zenithicus. A comparison with 

 the former is given on page 357. Alpense and zenithicus differ most conspicuously 

 in the length of the mandible, the pigmentation of the maxillary, the position of 

 the premaxillaries, and the size attained. In alpense the lower jaw usually is longer 

 than the upper, whereas zenithicus usually has the lower jaw shorter than the upper 

 and included within it, and 6 per cent of the individuals examined had pigment 

 on the maxillary as compared with 83 per cent for zenithicus. The premaxillaries 

 in alpense usually make an angle of 50° to 60° with the horizontal axis of the head, 

 and the dorsal contour of the head usually is a smooth curve, seldom broken at 

 the premaxillary attachment, while in zenithicus the angle becomes 60° to 70° and 

 the curve of the dorsal contour of the head is broken at the symphysis with the rostral 

 cartilage. Zenithicus seldom grows larger than 300 millimeters, while alpense com- 

 monly exceeds this limit. The state of development of the ova in females often 

 will serve as a valuable character. Alpense spawns about the middle of November 

 and zenithicus during the last of September and the first of October, so that the 

 ovaries of the females of the one species usually show more mature ova than those 

 of the other. Alpense differs from zenithicus in other characters, but the differences 

 are slight. The body of zenithicus, as a rule, is more pigmented, the head and body 

 shallower, the maxillary longer, and it usually has not more than 24 scale rows 

 around the caudal peduncle at its commencement, while alpense most often has more 

 than 24. 



The longjaw and blackfin of Lake Huron differ from one another in about the 

 same manner as the two species have been shown on page 365 to differ in Lake 

 Michigan. However, there is another difference observable in the Lake Huron 

 fish — namely, the size of the eye. The values for H/E are for nigripinnis (3.6) 

 3.9-4.2 (4.6), with 3 per cent more than 4.4, and for alpense (4) 4.5-4.9 (5.2), with 

 84 per cent more than 4.4. 



Small alpense are comparable with Tciyi and are distinguishable from them by 

 their shorter paired fins, fewer gill rakers, smaller eye, and less pigmentation. 

 Those characters that can be expressed numerically are compared below for all 

 Tciyi collected and for all alpense less than 21 centimeters in length: 



Gill rakers on the first branchial arch: 



alpense, (31) 33-37 (41), with 12 per cent more than 37. 



kiyi, (34) 36-40 (44), with 60 per cent more than 37. 

 H/E: 



alpense, (3.6) 3.8-4.1 (4.4), with 78 per cent more than 3.8. 

 kiyi, (3.3) 3.6-3.8 (4.3), with 21 per cent more than 3.8. 



