PREFACE TO THE REPORT OF 1884 ON THE CLADO- 
CERA AND COPEPODA OF MINNESOTA. 
In presenting what may be denominated a final report of the work 
done in this state upon the group of Crustacea best represented and, 
all things considered, most important, the author must admit that the 
term ‘‘final’’ refers only to his own opportunities and the limitation 
of time imposed by circumstances. 
While a comparatively large proportion of all the species existing 
within our limits have been examined during the progress of these 
investigations, there undoubtedly remain many additional and curious 
forms to reward the search of the student. A great variation in the 
degree of completeness with which the different genera and species 
_ have been treated will be observed, due in part to the circumstances 
under which they were studied and frequently to the poverty of ma- 
terial. The entomostracean fauna is quite different at different sea- 
sons, and a complete knowledge of even our local fauna requires a long 
period of observation. Even the dead of winter is a favorable time to 
study some groups. The late autumn is, perhaps, the most favorable 
opportunity; for then, in one group, the sexual activities are just at 
their height and both sexes may be studied. A number of Cladocera 
are restricted to this season. There are a number (how large it is not 
yet possible to tell) of species in both groups which are to be sought 
by night, though no phosphorescent species are yet known, Our 
larger and, especially, deeper lakes have a quite different fauna from 
the shallow pools and rivers. In general, the flowing waters are poor 
in Entomostraca. The Cladocera or shelled Entomostraca have here 
received a large share of attention, and more particularly the Lyn- 
ceide, which are the most minute of Arthropods. This study has been 
rewarded with an unexpectedly large number of forms, and a particu- 
larly large number of species identical with those of Europe and else- 
“where. Professor Birge is the only American writer who has 
attempted this group, and his valuable work has made us familiar 
with the more striking new species. A few new species are included 
in our list and several varieties hidly yet known in Europe. ‘The 
