DISCOVERY OF THE GREAT LAKE TROUT 687 



of the elements are shown. The parasphenoid is also preserved. 

 It is seen on the under side of the posterior portion of the skull 

 roof, which is the only part of the upper skull surface preserved. 

 This element also agrees closely with that of the existing species. 



The discovery of fossil remains of Cristivomer is interesting but 

 not unexpected; for the existing species has a wide range in the 

 colder waters of north temperate America, extending into the 

 sub-arctic region. Jordan gives the distribution as follows: "All 

 the larger lakes from New England and New York to Wisconsin, 

 Montana, the Mackenzie River, and in all the lakes tributary to 

 the Yukon in Alaska." 1 



From the extent of this range one would have inferred that the 

 species must have had a long time in which to "spread out" over 

 such an area, and hence that it dated back to at least Pleistocene 

 times. The finding of this specimen proves that this was the case. 

 It shows, moreover, that the genus existed during glacial times in 

 the same region as today, so that its antecedent history — whether 

 it arose in the same region, or wandered into it from somewhere 

 else — dates back to an even earlier time. 



The specimen is preserved in the collection of the Wisconsin 

 Geological Survey. The following measurements may be of use 

 for future reference: 



Vomer 



Length 44 mm. 



Width at neck 12 



Premaxilla (Left) 



Length, measured along toothed edge 33 



Height, at posterior end 27 



Maxilla (Right) 



Total length . .' 105 



Length exclusive of anterior process (measured along 

 toothed margin) 95 



Mandible 



Both are defective posteriorly; the left as far as pre- 

 served measures 95 



1 Jordan, Guide to the Study of Fishes, II, 115. 



