68 NORTHERN FISHES 



American Brook Lamprey, Entosphenus lamottenii (LeSueur) 



2. Parasitic species; adults retaining a functional digestive tract until a length 

 of more than 7 inches is attained; teeth well developed, regular on posterior 

 field of buccal funnel; length of buccal funnel contained 7.7-16.9 times in 



total length 3 



Nonparasitic species; adults with nonfunctional digestive tract; total length 

 less than 7 inches; teeth more or less degenerate, at least on posterior field 

 of buccal funnel; length of buccal disc contained 1.5.4-^7.7 times in total 



length ., 



. . . .Michigan Brook Lamprey, Ichthyomyzon jossor Reighard and Cummins 



3. Circumoral teeth, with rare exceptions, all unicuspid (single pointed) ; myo- 

 meres (body segments) between last gill-slit and anus usually 49-52; trans- 

 verse lingual lamina moderately to strongly bilobed 



Silver Lamprey, Ichthyomyzon unicusjris Hubbs and Trautman 



Circumoral teeth in part, usually 6-8, bicuspid (double pointed); myo- 

 meres between last gill-slit and anus usually 51-58; transverse lingual 



lamina usually linear or weakly bilobed 



Chestnut Lamprey, Ichthyomyzon castaneus Girard 



GENUS Ichthyomyzon Girard 



These are medium-sized lampreys. The adults may be distinguished 

 from the genus EntospJiemis by the presence of a single emarginated 

 dorsal fin which is continuous with the tail, or caudal, fin. 



Figure 1 . Silver lamprey, Ichthyomyzon unicuspis, 8 inches long. 



SILVER LAMPREY 



Ichthyomyzon unicuspis Hubbs and Trautman 



The silver lamprey (Figure 1) is a species recently separated by 

 Hubbs and Trautman (1937) from material previously known as the 

 western lamprey, Ichthyomyzon concolor Kirtland. It is a small, slender, 

 eellike animal, 8 to 10 inches long, with a large, funnel-shaped liuccal 

 cavity greater in diameter than the body. The circumoral teeth are 

 entirely unicuspid. 



Silver lampreys have been reported by Hubbs and Trautman from 

 the Great Lakes including Superior, from Lake of the Woods, and 

 from the Upper Mississippi drainage. Most of the lampreys in the 

 collections of the University of Minnesota from Lake Pepin and Lake 



