GREAT LAKES COREGONIDS 



553 



grounds of the trout 7 miles ENE. of the Alpena can buoy in 15 fathoms. When 

 lifted on November 2 these nets had, among other fish, 41 pilot. The number of 

 pilot caught is not great, but there are reasons, perhaps, why the fish were not abun- 

 dant. First, the trout had not yet left the grounds, and second, the majority of the 

 pilot were already moving onto their own spawning grounds in 3 to 5 fathoms. Of 

 the 41 fish, 21 had nothing in their stomachs, 12 had trout eggs, and 8 had other food. 

 Thus, 29 per cent of the fish taken are known to have been feeding on trout eggs and 

 19 per cent were feeding on other things. The remaining 52 per cent may or may 

 not have eaten eggs. The nets had been set for about 48 hours, and if these fish had 

 been caught in the earlier half of this period, there would have been ample time to 

 digest the eggs if they had eaten them. All the fish were alive when taken. The 

 results obtained on this occasion are by no means conclusive, and many more data 

 must be obtained before the pilot can be condemned as a spawn eater. 



Prosopium quadrilaterale of Lake Superior 



The pilot of Superior agrees in its principal characters rather closely with that of 

 Michigan. The principal characters that can be expressed numerically are com- 

 pared below: 



Gill rakers on the first branchial arch: 



Michigan, (15) 16-18 (19) . 86 



Superior, (15) 16-18 (20) « 

 Lateral-line scales: 



Michigan, (84) 87-95 (100). 



Superior, (84) 86-93 (98) . 88 

 L/H: 



Michigan, (4.9) 5.2-5.4 (5.6). 

 Superior, (4.6) 4.8-5.1 (5.3). 



H/E: 



Michigan, (3.9) 4.3-4.6 (5). 

 Superior, (4) 4.2-4.6 (5.1). 

 Pv/P: 



Michigan, (1.8) 1.9-2.2 (2.3). 

 Superior, (1.5) 1.7-1.9 (2.1). 

 Av/V: 



Michigan, 2.1-2.3 (2.5). 

 Superior, (1.9) 2-2.2 (2.5). 



It appears that the Superior specimens differ from those of Michigan chiefly in 

 having a proportionally longer head and longer paired fins, especially pectorals. 



The color in life is like that of Michigan specimens. Fingerlings are less brilliantly 

 colored than adults. A description of these small fish is given under "Size varia- 

 tions." In spirits the coloration averages about as in Huron specimens. 



There are indications of pearl organs on both male and female specimens col- 

 lected on October 1, 1921, at Rossport, Ontario, and it is likely that in the breeding 

 season both sexes are conspicuously pearled, as is known to be the case in the Huron 

 form. 



VARIATIONS 



Racial variations. — There are no data on local variations. 



Size variations. — The depth increases and the head, eye, and ventrals decrease 

 with age, as in the Lake Huron form. For 17 individuals ranging from 65 to 200 

 millimeters, the L/H ratio is 4.3-4.9 (5.2). This value for the group of specimens less 

 than 300 millimeters and for that of more than 300 millimeters is (4.6) 4.8-5.1 (5.3), 



>e Figures for Michigan, except those for scales, are based on an examination of 34 specimens ranging in length from 200 to 419 

 millimeters. Lateral-line scales have been counted for 65 specimens. 



■ Figures for Superior are based on an examination of 63 specimens ranging in length from 236 to 387 millimeters. 

 11 One specimen with 74. 



