544 



BULLETIN OF THE BUREAU OF FISHERIES 



The two openings of each nostril are separated by a single flap. (Fig. 27.) The 

 exposed area of the scales of the lateral line is conspicuously smaller than that of 

 those of the adjacent rows. The gill rakers on the first branchial arch are less than 

 21 and more than 13; the length of the longest is rarely more than 5 per cent of the 

 head. There are no vestigial teeth. The prefrontal bone is but little developed and 

 does not extend much beyond the anterior edge of the pupil. The cranial carina 

 does not extend to the frontal-parietal suture. 



PROSOPIUM QUADRILATERALE Richardson 



Pilot, Menominee, Round Whitefish, Frostfish, Cisco, Grayback, Cross Whitefish, Lake 



Minnow (Fig. 30) 



Coregonus quadrilateralis Richardson, 1823, pp. 714-716 pi. 25, fig. 2, "small rivers about Fort 

 Enterprise and in the Arctic Sea"; Evermann and Smith, 1896, pp. 296-297, pi. 16, New England 

 to Alaska; Jordan and Evermann, 1911, pp. 38-39, PI. VII, Alaska and upper Great Lakes to 

 New England. 



Prosopium quadrilaterale Dymond, 1926, pp. 54-55, PI. VIII, fig. 1, Lake Nipigon. 

 Coregonus nov-anglix Prescott, 1851, p. 342, Lake Winnepesaukee. Probably also Sea Gwiniad, 

 Pennant, 1792, p. ccxcviii, Hudson Bay. 



The species was described from specimens collected in "small rivers about 

 Fort Enterprise and the Arctic Sea." No material from the type locality is available 

 for examination, but there is little doubt that Richardson's description is of a Pro- 

 sopium of some sort, and it is probable that our Great Lakes forms are very closely 

 related to it. For the present, then, the specific name quadrilaterale is retained 

 for them. 



The pilot occurs in all the lakes of the Great Lakes series except Erie, and in Lake 

 Nipigon. The representatives of the species in one lake resemble those in another 

 very closely, the differences between them being chiefly such differences as are evident 

 between mature and immature individuals in any one of the lakes. No complete 

 account of the natural history of the species is available for any of the lakes, but 

 such details as are known indicate that the habitat selected is the same throughout 

 the basin; and it is probable, further, that the breeding habits, making due allowance 

 for differences in latitude, which probably affect the time of spawning, are the same. 

 The flesh is not of the best, and the species is of relatively little or no commerical 

 importance anywhere. 



Prosopium quadrilaterale of Lake Michigan 



The body is subterete, much elongated, little compressed (except at the snout 

 and tail — much less compressed than the whitefish), and uniformly tapered. Its 

 greatest depth is through a point at the front of the dorsal. In adults this measure- 

 ment is usually about 20 to 22 per cent of the length, though in the largest examples, 

 especially gravid females, it commonly becomes 24 per cent. Owing to the moderate 

 depth of the body, its profiles are gently and uniformly curved. The head is very 

 small and is contained (4.9) 5.2-5.4 (5.6) 81 times in the total length of the body. 

 In side view the outline of the head is roughly ovoid, its dorsal contour curving sharply 

 downward from a point between the orbit and the nares, so that the snout is always 



«i These and succeeding figures, unless otherwise marked, are given for 34 collected specimens ranging from 200 to 419 milli- 

 meters in length. 



