GREAT LAKES COREGONIDS 



353 



Johannse is at once separable from artedi by the fewer gill rakers on the first 

 branchial arch, which are not known to be more than 36 in the former and not less than 

 41 in the latter; by the body shape, which in johannse is less elliptical, as seen from 

 the side; and by the longer paired fins. The comparative values for Pv/P and Av/V 

 follow : 



Pv/P: 



johannse, (1.5) 1.6-1.8 (2.1), with 16 per cent more than 1.8. 

 artedi, (1.6) 1.9-2.2 (2.6), with 94 per cent more than 1.8. 

 Av/V: 



johannse, (1.1) 1.2-1.5 (1.6), with 6 per cent more than 1.5. 

 artedi, (1.4) 1.6-1.8 (2.3), with 89 per cent more than 1.5. 



Johannse has usually no pigment on the maxillary, premaxillaries, and mandible, 

 while in artedi these parts are pigmented; the general color of the latter, including 

 the fins, is much darker. Johannse has a relatively longer snout and maxillary, a 

 smaller eye, larger head, more body depth, and more pectoral rays. Johannse spawns 

 in August to September and artedi in November, so that often at least the females 

 •can be separated by the state of development of the sex organs. 



GEOGRAPHICAL DISTRIBUTION 



Data on the occurrence of the chub in Lake Michigan are assembled in Table 

 16 and are shown platted on a map of the lake in Figure 4. There are 17 records 

 made by me from the commercial chub nets of 2% to 2% inch mesh set out of 13 

 ports on the lake. Comparison with a similar table prepared for hoyi (Table 56) 

 makes obvious the fact that while the chub may be taken out of most of the ports 

 visited, it is by no means always present in all the lifts made from these ports. The 

 conclusion may be drawn, however, that the chub occurs throughout the lake at 

 suitable depths and on suitable bottom. 



BATHYMETRIC DISTRIBUTION 



The records in Table 16, from the commercial nets set for deep-water Leucich- 

 thys or "chubs," show johannse, to have been taken at depths of 30 to 90 fathoms. 

 Certain other examined lifts of these small-meshed nets, made at depths of 22 to 50 

 athoms, took no johannse, but some of these were made on or near the spawning 

 grounds of other species, and it is understandable that johannse should not have 

 occurred among them. Lifts of this kind were made on March 24, 1919, off Mil- 

 waukee, Wis., in 50 fathoms, and on March 2, 1921, 21 miles NNW., and on March 

 4, 1921, 15 miles NW. by N. % N. of Michigan City, Ind., in 28 to 30 fathoms on 

 the spawning grounds of hoyi; on November 15, 1920, 20 miles ESE. of Milwaukee 

 in 28 to 35 fathoms, and on November 19, 1920, 10 miles NNW. of Michigan City, 

 Ind., in 18 fathoms, and 173^ miles NW. by N. % N. in 32 fathoms on the spawning 

 grounds of zenithicus. Sets of nets of suitable mesh, but which were probably in 

 too shallow water or on grounds unsuitable for johannse, were made on August 16, 

 1920, in Green Bay off Little Sturgeon and 8 miles south of Green Island, Wis., in 

 11 and 16 fathoms; on August 18, 1920, 4 miles west of Boyer Bluff, off Washington 

 Harbor, Wis., in 18 to 24 fathoms; on September 24, 1920, 9 miles NNE. of Mil- 



