STATE GEOLOGIST. 65 



middle. The spine is long, the claws smooth, the abdominal pro- 

 cesses united and the shell transparent. The eye is near the end 

 of the rounded head and is large; the pigment fleck was apparently- 

 absent. Found with Daphnia minnehaha in a shallow swampy 

 pool in autumn. 



Family Bosminid^. 



The sole genus of the family, Bosmina, contains over a dozen 

 nominal species which are among the most difficult to define of 

 any cladocerans. The number is here reduced to nine and the 

 probable position of the rejected species is indicated. This is not 

 done because the author presumes upon the slender material at 

 hand to revise the genus; but simply from the fact that the descrip- 

 tions of the earlier writers do not permit a proper discrimination ; 

 so that this necessity is entailed upon any one who would give a 

 birds-eye view of the members of the genus. The B. diaphana is 

 founded upon a different twist in the antennules and no hesitancy 

 is felt in uniting it with Sars' B. lilljeborgii. The other species, 

 B, brevirostris and B. nitida, are omitted simply because there 

 seems to be no way of separating them satisfactorily from B. mari- 

 tima and B. obtusirostris respectively. Three species have been 

 found in Minnesota, but practically no attention has been given to 

 the genus here. 



Bosmina macrorhyncha found in Egypt is not here included, its 

 description being inaccessible to me. 



B. Isevis, Leydig, seems simply a smooth condition of other spe- 

 cies. Whether B. curvirostris, Leydig, is or is not valid must, so far 

 as I am concerned, remain at present doubtful. 



Genus Bosmin-a, 



A. Shell extending into a spine behind. 



(a) Antennae curved outward. 



1. Bosmina cornuta , Jurine. 



(b) AntenuEe not curved outvyard, 



L Shell reticulated, at least in part. 

 t Flagellum midway betvi'een eye and the sensory sette of antennas. 



2. Bosmina longirostris, Mueller. 

 tt Flagellum nearer eye. 



3. Bosmina maritima, P. E. Mueller. 



4. BosminaJoncrispina, Leydig, (B. brevirostris?) 

 II. Shell striate, 



t Antennules long. 

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