GREAT LAKES COREGONIDS 



387 



which in zenithicus number (33) 36-39 (42), with 10 per cent more than 39, as 

 compared with (40) 42-46 (48) for hoyi. From the few small specimens of zenithicus 

 at hand, it appears also that they have relatively smaller eyes and relatively shorter 

 paired fins, especially ventrals. 



Zenithicus is distinguishable from artedi and nipigon by having many fewer 

 gill rakers and a longer snout and maxillary. Comparative figures follow: 



Gill rakers: 



zenithicus, (33) 36-39 (42), with 4 per cent more than 40. 

 artedi, (41) 46-49 (53). 

 nipigon, (54) 56-59 (66). 

 H/S: 



zenithicus, (3) 3.2-3.4 (3.8), with 1 per cent more than 3.6. 

 artedi, (3.5) 3.7-3.9 (4.2), with 91 per cent more than 3.6. 

 nipigon, (3.3) 3.5-3.8 (4), with 55 per cent more than 3.6. 

 H/M: 



zenithicus, (2.2) 2.3-2.5 (2.8), with 17 per cent more than 2.5. 

 artedi, (2.5) 2.7-2.8 (3), with 98 per cent more than 2.5. 

 nipigon, 2.5-2.7 (3.1), with 78 per cent more than 2.5. 



Zenithicus is less pigmented on body and fins and has, as a rule, a shorter and 

 more included mandible. It is distinguished further from nipigon by its less depth 

 of body and by the fact that it seldom grows longer than 300 millimeters, while 

 specimens of nipigon commonly exceed that limit. 



GEOGRAPHICAL DISTRIBUTION 



In Table 26 are collected my data and those of the specimens examined from the 

 University of Toronto collection on the distribution of zenithicus in Lake Nipigon. 

 They are platted on the chart of the lake in Figure 2. All are derived from the use of 

 special small-meshed nets set during the course of a survey of the fishes of the lake. 

 The records are distributed widely enough to warrant the conclusion that zenithicus 

 occurs throughout the lake where there are suitable conditions. 



BATHYMETRIC DISTRIBUTION 



Zenithicus was present in two of the three sets made by me in Lake Nipigon. 

 On July 25, 1922, off the source of the Nipigon River, in 10 to 15 fathoms, zenithicus 

 made up 13 per cent of the catch; and on the following day, off Macdiarmid, in 30 

 fathoms, 43 per cent of the take was of this species (records 16 and 1). (For a 

 statement of the comparative abundance of the coregonids in these lifts, see p. 409.) 

 No zenithicus occurred in the lift made on July 28, 1922, off Livingston Point, in 56 

 fathoms. The specimens from the University of Toronto collection, so far as is 

 known, were taken at depths of 6 to 54 fathoms, but chiefly in less than 30 fathoms. 

 The species probably prefers water of moderate depth. 



BREEDING HABITS 



Of five specimens collected on October 26, 1922 (record 19), one female was 

 spent and the other individuals were nearly ripe, so that it may be assumed the 

 spawning season falls around the first of November. Nothing else is known of the 

 breeding behavior of the species in Lake Nipigon. 



