FISHES OF LAKE SUPERIOR. 817 



are mentioned by Dr. Richardson : an Esox Lucius and an Usox 

 Estor Lesu. Now the species of Lake Superior is not the Lucius 

 of the Fauna Boreali-Americana, as we might infer by comparing the 

 descriptions. In regard to this, we could entertain no doubt. As 

 for the Esox Estor of Dr. Richardson, we allow that we have doubts 

 whether or not the author of the Fauna Boreali-Americana had the 

 true Esox Estor Lesu., or perhaps my Esox Boreus, from^Lake Su- 

 perior. The description which he gives of it* is too incomplete to 

 enable us to recognize it ; the more so, as that description is made 

 with reference to Esox Lucius, which is found to be quite different. 

 Only two characters occur which may be considered to have some 

 value ; but, strange to say, these two characters are found united in 

 none of the species which I know. I mean, first, the form of the 

 scales, which are as high as they are long, a character which we 

 find in the true Esox Estor Lesu. But, again, the scales would be 

 much smaller in the species which Dr. Richardson had in view. 

 The Esox Estor Lesu. is the species which has the least number of 

 scales on the cheeks and opercula ; but Dr. Richardson gives for his 

 E. Estor two rows of scales, which descend along the anterior mar- 

 gin of the operculum until they attain the upper angular process of 

 the suboperculum. It is therefore possible that the species referred 

 to Esox Estor by Dr. Richardson was neither the Esox Estor Le- 

 sueur, nor my Esox Boreus, but a species distinct from all others, 

 as the small size of its scales seems to indicate. 



Esox Boreus, Agass. 



When marked external zoological characters are wanting in a 

 group, on account of its uniformity, it becomes necessary to resort 

 to another series of facts. When the object is to find the place 

 which a certain family occupies in its order or in its class, compara- 

 tive embryology and palaeontology will often answer the purpose as 

 completely as an anatomical investigation, and even with more pre- 

 cision. If, on the contrary, we have to do with the distinction of 

 species, we may in such cases have recourse to comparative anat- 



* Fauna Boreali-Americana, p. 127. 



