GREAT LAKES COREGONIDS 



315 



forms that had been considered identical have different numbers of gill rakers. 

 He points out the specific importance of the shape of the snout, the number of gill 

 rakers, and of biological data. Later workers on the coregonids have paid heed 

 to Nusslin but still have given too much weight in their diagnoses to differences in 

 proportions and other similar characters which may be influenced by the environ- 

 ment. In fact, little effort has been made to determine, by a study of the variability 

 of the external characters, what relation, if any, existed between them and the 

 environment. 



VARIABILITY OF INDIVIDUAL CHARACTERS 



My own work on the forms in the Great Lakes, based on measurements of some 

 10,000 specimens from many localities and cursory inspection of some hundreds of 

 thousands, has involved, then, of necessity, an attempt at analysis of the variability 

 of these forms. The effort has been made to study all possible characters in order 

 to learn which ones so vary that they are of little or no use in classification and 

 which ones are sufficiently stable to be of use. At the same time the available 

 data on spawning seasons, bathymetric and geographic distribution, seasonal move- 

 ments, and other biological factors have been studied in order to learn whether they 

 are correlated with the structural characters found usable in classification. 



Fig. 9. — Body outline of the typical Lake Erie whitefish 



Body Contour 



Leucichthys. — Two groups may be separated according to contour or form of 

 body as seen from the side. In the first of these the body is more or less perfectly 

 elliptical. The species included are alpense, zenithicus, reighardi, hoyi, artedi, and 

 nipigon. Of these, Jioyi, reighardi, nipigon, and the albus and manitoulinus sub- 

 species of artedi are least elongated and the typical artedi is most elongated. In the 

 second group, comprising johannae, nigripinnis, and Tciyi, the anterior dorsal profile 

 rises rapidly for two-thirds its extent and continues thence to the dorsal fin as a nearly 

 horizontal line. In nigripinnis the anterior ventral profile extends in a direction 

 similar to the dorsal, so that the anterior half of the body in this species is distinctly 

 the deeper. In johannse the tendency of the contour line between the dorsal and the 

 adipose to become straight further interrupts the symmetry of the lateral profile. 



