2 U.S. NATIONAL MUaEUM BULLETIN 271 



specialists. Perhaps it will stimulate monographic studies of famiUes 

 and genera. It may be of greatest use to those students who must 

 make generic determinations of their material without adequate 

 hbrary faciUties; it should restrict bibhographic needs to small numbers 

 of pubhcations which can be borrowed more easily than can the entire 

 literature. An index to the species of Gammaridea (J. L. Barnard, 

 1958a) may be of some help. An expanded and more useful index is 

 now in preparation. 



Brief sections on distribution, faunules, and evolution are presented 

 in hopes of stimulating further inquiry into these fascinating but poorly 

 studied topics. Our knowledge of anatomy (especially musculature), 

 functional morphology, behaviour, food habits, indeed general ecology 

 is rudimentary. 



The identification system proposed herein requires familiarity with 

 a basic gammaridean plan similar to that exemplified by some members 

 of the Gammaridae. These gammarids may be the most primitive 

 grade of living Amphipoda. A knowledge of their structure is vital to 

 an understanding of the unfolding of the complex network of speciali- 

 zations found in other gammaridean families. The lines of evolution 

 from gammarid-like ancestors, so ill understood, are not only manifold 

 but they confuse identification procedures. At times the specialist is 

 confronted with the feeling that most of the "missing links" in 

 Amphipoda are still aUve. Only a few families are so remote morpho- 

 logically from the Gammaridae that they are instantly recognizable. 

 With a few exceptions the specialization of gammaridean families is 

 a result of the loss of morphological complexity. 



The basic gammaridean is illustrated in figures 1 and 2 and described 

 on p. 50. Families other than the Gammaridae are provided with 

 short diagnoses which include only definitive and exclusive differences 

 from the basic gammaridean. Some of these diagnoses are identical 

 among several families. Those taxa are further distinguished by 

 intercomparison of their descriptions and by reference to paragraphs 

 on relationship. Part of each diagnosis is a reference to a related (or 

 superficially similar) family. 



Diagnostic characters of the families are illustrated in a group of 

 boxes (figs. 3-53). Instructions for identification procedures using 

 these tools are presented in following pages. 



Acknowledgments 



This work was compiled during the writer's tenures at the Allan 

 Hancock Foundation, the Beaudette Foundation of California, and 

 the Smithsonian Institution, to which institutions and their adminis- 

 trative heads my gratitude is expressed. Mrs. Dorothy M. Halmos of 



