GREAT LAKES COREGONIDS 



365 



upper jaw, while in zenithicus it is usually shorter and included within it. In the 

 former the premaxillaries are immaculate or but faintly pigmented in half of the 

 ispecimens examined and the maxillary is almost always immaculate; the pre- 

 maxillaries and maxillary usually are pigmented in the latter. The depth of the head 

 is greater and the length of the maxillary less in alpenx, so that the value of the head 

 depth (HD) divided by the maxillary length (M) is (1 .4) 1 .5-1 .7 (1 .8), with 79 per cent 

 more than 1.5 for alpenx, and (1.3) 1.4-1.6 (1.7), with 25 per cent more than 1.5 for 

 zenithicus. The depth of the body in alpenx is likewise more; L/D equals (3.3) 

 3.9-4.3 (4.9), with 11 per cent more than 4.3 in alpenx, and (3.6) 4.2-4.6 (5), with 

 58 per cent more than 4.3 in zenithicus. Zenithicus seldom is larger than 300 milli- 

 meters, while examples of alpenx that exceed this limit are met frequently. The 

 dorsal contour of the head is straighter, also the shape of the head in side view less 

 broadly triangular, and the body slightly wider in zenithicus. 



Alpenae. differs from reighardi in about the same way that it differs from zenithi- 

 cus— in points of pigmentation and length of mandible — but pigmentation is still 

 more abundant in reighardi; and in addition to being present on the premaxillaries 

 and maxillary it is also abundantly present on the mandible and occasionally on the 

 abdominal fins. Moreover, alpenx has more gill rakers on the first branchial arch, 

 longer pectoral fins, a narrower body, more lateral-line scales, and attains a greater 

 size. Alpenae spawns in November while reighardi spawns in May or June, so that 

 the state of ripeness of the sex products often may serve as a distinguishing character. 

 A comparison of certain of the above-mentioned characters follows: 



Gill rakers: 



alpenx, (33) 36-43 (46), with 66 per cent more than 38. 



reighardi, (30) 34-38 (43), with 13 per cent more than 38. 

 Lateral-line scales: 



alpenas, (71) 78-85 (96), with 47 per cent more than 81. 



reighardi, (66) 72-81 (96), with 12 per cent more than 81. 

 Pv/P: 



alpenas, (1.6) 1.9-2.2 (2.5), with 9 per cent more than 2.2. 

 reighardi, (1.7) 2-2.5 (2.8), with 41 per cent more than 2.2. 



The differences between alpenas and nigripinnis are about the same as between 

 nigripinnis and johannae. The difference in the number of gill rakers is not so 

 sharp, however; while nigripinnis may have 41 but seldom less than 44, alpenae may 

 have 46 but seldom more than 43. In addition, alpenx has shorter paired fins, a 

 heavier and much paler mandible, and a much more elliptical body outline (as seen 

 from the side) than nigripinnis. The comparative figures for fin length follow: 



Pv/P: 



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

 nigripinnis, (1.5) 1.6-1.8 (2.2), with 18 per cent more than 1.8. 

 Av/V: 



alpenx, (1.2) 1.4-1.7 (1.9), with 80 per cent more than 1.4. 

 nigripinnis, 1.2-1.5 (1.6), with 28 per cent more than 1.4. 



Alpenae also spawns a month earlier than nigripinnis. 



Alpenae grows much larger than Jciyi, so that only the smaller specimens are 

 •comparable with Jciyi. The species differ chiefly in body shape, which in alpenx is 



