8 MICHIGAN FISH COMMISSION— BULLETIN NO. 5. 



rior and Lake Erie. It occurred in the collections from Lake St. Clair 

 and the Detroit River, but not abundantly. In the Lake Michigan col- 

 lections it was a common species, but not nearly so numerous as D. 

 minutus. I found it in none of the smaller lakes except Round Lake and 

 Pine Lake. 



Diaptomus minutus Lilljeborg. 



Plate VII, figs. 



1889. D, minutus DeGuerne and Richard, (Lilljeborg) p. 50, pi. I, figs. 

 5, 6 and 14, pi. Ill, fig. 25. 



1891. D. sicilis vfir. imperfectus Forbes, p. 703. 



' 1891. " l^^fersh, p. 2L2. 



1893. " " Marsh, p. 199, pi. IV, figs. 1 to 3. 



D. minutus is, perhaps, the most common of all the Diaptomi in the 

 collections from Lake St. Clair and the Great Lakes. With D. sicilis and 

 D. Ashlandi it forms the great bulk of the Crustacea in the limnetic col- 

 lections. While I have found it in one or two of the Wisconsin lakes, it, 

 like the two preceding species, has not so far been found in any of the 

 Michigan waters which do not have direct connection with the Great Lakes. 

 The three species may be fairly considered as characteristic of the fauna 

 of the Great Lakes. 



It is with considerable hesitation that I have considered Forbes's imper- 

 fectus identical with minutus. One can not be certain of the identity of 

 the two forms from the description given by Forbes, and yet from the 

 localities which he gives for his variety, it seems very probable that the 

 two are the same. He speaks of it as common in Lake Superior and Lake 

 Michigan, and in some adjacent lakes, and in Lake Geneva. Inasmuch as 

 D. minutus is so common in the Great Lakes it is not at all probable that 

 it has been overlooked by so accurate an observer as Professor Forbes, 

 and as he reports imperfectus as an abundant form, I think the probabili- 

 ties are that imperfectus is a syuonym of minutus. 



Diaptomus oregonensis Lilljeborg. 

 Plate VII, fig. 5. 



1889. D. oregonensis DeGuerne and Richard, (Lillj.) pi. II, fig. 5, pi. 



Ill, fig. 8. 



1893. " " Marsh, p. 200, pi. IV, figs. 4 and 5. 



D. oregonensis is the common limnetic species of the smaller lakes. It 

 occurs in the Great Likes, but not abundantly, while in the smaller bodies 

 of water it usually form3 the larger part of the limnetic fauna. 



