THE FRESH-WATER AMPHIPODA OF NORTH AMERICA. By Ada L. Weckel,, Of Moline, Illhiok. All the species of Amphipoda known to occur in the fresh waters of North America were described by Prof. Sidne}' 1. Smith in his report on the Crustacea of the Fresh AVaters of the United States, pub-lished in 1S74. Previous to that report practicalh^ no work had been done on the fresh-water forms belonging to this group. Since then many new species have been described, and the present paper is intended to include descriptions of all of the species of Amphipoda now known to occur in the fresh waters of North America. Only two species are here described for the first time, but as I have had the opportunity of examining specimens — in some cases the types — of most of the known forms, it was thought best to redescribe and figure them. The genera and also the species, in several instances, were in a state of confusion; consequently an extensive synon3'my of each species described has been included. A bibliography has also been added which lists the principal papers dealing with the amphipod fauna of the region covered by this paper. I am greatly indebted to Dr. S. J. Holmes, of the University of Wisconsin, under whose direction this work was conducted, for many courtesies received during the preparation of this paper. My thanks are due also to Prof. S. A. Forbes for the loan of a large collection of material from the Illinois State laboratory of natural history. A large number of specimens were ol)tained from the United States National Museum, and the valuable aid thus received is gratefully acknowledged. KEY TO FAMILIES AND GENERA. A. First antenntP with secondary flagelluin; iifth pencopods shorter than preceding; two rami of third uropods nearly equal; second gnathopods smaller than first Lysianassid.e. Pontoporeia, p. 26. AA. First antennfe with secondary flagellum; fifth per;eopods longer than the pre-ceding; second gnathopods generally larger than the first Gammakid^e B. Telson cleft; uropods biramous. 0. Inner ramus rudimentary; telson cleft not more than three-fourths distance to base. Proceedings U. S. National Museum, Vol. XXXII— No. 1507. 25
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