PROC. BIOL. SOC. WASH. 104(2), 1991, pp. 253-268 REVISION OF IPHIMEDIIDAE AND SIMILAR FAMILIES (AMPHIPODA: GAMMARIDEA) C. O. Coleman and J. L. Barnard Abstract.— The amphipod families Acanthonotozomatidae, Amathillopsi-dae, Astryidae, Epimeriidae (=Paramphithoidae), Iphimediidae, Ochlesidae and Stilipedidae are rediagnosed and three new families, Acanthonotozomel-lidae, Dikwidae, and Odiidae are described. New keys distinguish these fam-ilies; other similar families, Lafystiidae and Laphystiopsidae are diagnosed and included in the keys. In the process of rediagnosing the Och-lesidae Stebbing, 1910 (see Coleman & Barnard 1991a), as a family distinct from Iphimediidae, we determined that other al-terations to the taxonomy of the Iphime-diidae and Epimeriidae were necessary. Our contribution here offers a different division than used in the past based on characters not previously used or inconsistently used to define these groups. For example, we found relatively good consistency of char-acters on incisors, rakers, gnathopods and coxae in proposing this new division of the taxa. Discussion By using characters other than reduction of maxillipedal palp, we are able to tighten the diagnosis of Ochlesidae, but this re-quires, at the same time, the removal of the genera Odius and Postodius from the Iphi-mediidae to form the contents of a new fam-ily Odiidae, the removal of the peculiar Di-kwa from its paramphithoid-iphimediid associations to form a unique family Dikwi-dae, and the reinstatement of the Amathil-lopsidae (an old family synonymized with Epimeriidae some years ago). The genera Parepimeria Chevreux (1911) and Parepi-meriella Schellenberg (1931) are removed to the Pleustidae. By removing the above contents from the two families, the diag-nosis of Epimeriidae becomes strengthened and these amphipods can be distinguished more discretely from Iphimediidae, without resorting to the difficult judgment about the conical or quadrate shapes of the mouthpart group. Within the Iphimediidae two prin-cipal groups remain: those genera similar to Iphimedia and those genera similar to Acan-thonotozoma. These two groups are distin-guished and the Acanthonotozomatidae are revived. The new family Acanthonotozo-mellidae are split away from Acanthono-tozomatidae. Methods All diagnoses presented herein follow the format of comparison to the model amphi-pod known as the "basic gammaridean" pubUshed by Barnard (1969:50, figs. 1, 2). The formula for setae on the mandibular palp was invented by Stock (1974). Two keys with different starting points are pre-sented. To account for possible differing in-terpretations of certain characters some taxa are entered twice in the keys. For example, Dikwidae are entered twice to treat the al-ternatives of coxa 1 acuminate and tapering, or subtruncate and not tapering. Key I to the Families of the Iphimediidae and Similar Taxa 1 . Mandibular rakers present 2 -Mandibular rakers absent 10 2. Coxa 1 truncate, not pointed or ta-pering 3
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