396 



BULLETIN OF THE BUREAU OP FISHERIES 



Only small zenithicus can be confused with Tciyi as examples of the latter of 

 greater size than 249 millimeters have not been seen. Small zenithicus may be dis- 

 tinguished from Tciyi by their included mandible, which is usually longer than the upper 

 jaw and with a symphysial knob in Tciyi; by their more fusiform body, their smaller, 

 less triangular head, which in zenithicus of less than 200 millimeters in length is con- 

 tained (3.7) 4-4.2 (4.4) times in the head length, with 85 per cent more than 3.9, as 

 compared with (3.5) 3.6-3.9 (4.1) times, with 6 per cent more than 3.9 for Tciyi; and 

 their shorter paired fins, especially the pectorals. The value of Pv/P for small 

 zenithicus is (1.7) 2-2.2 (2.6), with 97 per cent more than 1.7, and for Tciyi (1.1) 

 1.4-1.7 (1.9), with 5 per cent more than 1.7. The eye, compared with the head 

 length, is also smaller in zenithicus. 



For a discussion of the distinctions between zenithicus and hoyi, see page 461. 



From artedi, zenithicus may be separated by its fewer gill rakers, longer head, 

 snout, and maxillary. These characters for the two species are compared below: 49 



Gill rakers: 



zenithicus, (34) 37-40 (44), with 49 per cent more than 39. 

 artedi, (40) 45-50 (53). 

 L/H: 



zenithicus, (3.9) 4.1-4.3 (4.5), with 1 per cent more than 4.4. 

 artedi, (4) 4.3-4.6 (5), with 57 per cent more than 4.4. 

 H/M: 



zenithicus, (2.3) 2.4-2.6 (2.7), with 3 per cent more than 2.6. 

 artedi, (2.6) 2.8-3 (3.3), with 96 per cent more than 2.6. 



H/S: 



zenithicus, (3.2) 3.4-3.7 (4), with 29 per cent more than 3.6. 

 artedi, (3.5) 3.7-4 (4.3), with 82 per cent more than 3.6. 



Zenithicus averages also fewer scales in the lateral line and longer paired fins, 

 and the mandible is better developed and more decidedly included within the upper 

 jaw. Zenithicus spawns in late September and artedi spawns in November, so that 

 the state of development of the sex organs, especially in females, also serves as a 

 character to separate the two species. 



GEOGBAPHICAL DISTRIBUTION 



All my data on the occurrence of this species in Lake Huron are assembled in 

 Table 30 and are platted in Figure 5. It is noteworthy that there are fewer records 

 for the short-jawed chub from the 2%-inch nets than for the longjaw or chub, but 

 that, on the other hand, there are many more records for it from the 43^-inch nets. 



Lake Huron proper. — Though the short-jawed chub has not always been found 

 in the lifts of the 2^-inch chub nets, the locations from which it has been taken 

 in general are not different from those that have yielded longjaws and chubs, and 

 thus the same conclusions on distribution are warranted for this form as for these 

 other fish. It may be stated, then, at least provisionally, that the species ranges 

 throughout Lake Huron in water of 14 to 100 fathoms. 



North Channel. — No specimens have been seen from the North Channel. Chubs 

 of some sort, however, are known to occur in the region (see p. 373). The chart shows 



41 Figures for zenithicus are based on fish 200 millimeters or more in length; for artedi on specimens 225 millimeters or more in 

 length, except in the case of gill rakers, which are given for all the specimens collected. The figures of the manitouiinus race are not 

 included. 



