540 



BULLETIN OF THE BUREAU OF FISHERIES 



in the University of Michigan collection. These fish ranged in length from 203 to 

 328 millimeters, and many of them were sexually mature. 



The body parts show great modification in all the specimens, aDd no e of them 

 closely resemble any whitefish taken in the Great Lakes. The most striking differ- 

 ences are changes in the shape of head parts. The head throughout is much deeper 

 than in normal whitefish, and its dorsal contour usually is decurved conspicuously 



c 



Fig. 31. — Comparison of the heads of the "mule whitefish" (A), a normal whitefish (B), and a New York aquarium specimen (C) . 

 The fish were about equal in size — A, 282 millimeters; B, 305 millimeters; and C, 315 millimeters 



anterior to the orbit. (See fig. 31, C.) The premaxillaries are often vertical in posi- 

 tion, which is not known to be the case in normally reared individuals. The head is 

 broader, especially across the snout, and the adipose is much larger usually. 



The characters that can be expressed numerically also are interestingly different. 

 All the specimens from the Great Lakes less than 300 millimeters long (many of them 

 less than 200 millimeters long), are combined for comparison in certain characters 

 with those of the New York aquarium. The complete figures are given below: 



