GAMMARIDEAN AMPHIPODA 37 



2 large and equal in length to, or scarcely shorter than coxa 3 ; outer 

 ramus of uropod 3 biarticulate ; telson cleft one eighth or more, usually 

 one third to three fourths. 



Genera. — Amhasiopsis K. H. Barnard,* Anonyx Kr0yer,* Aris- 

 tiojms J. L. Barnard, Elimedon, J. L. Barnard, Eurythenes Smith,* 

 Hippomedon Boeck, Lejndepecreoides K. H. Barnard, Neoambasia 

 Dahl,* Onisimus Boeck (some species), Paracentromedon Che\Teux 

 and Fage, Pseudonesimus Chevreux, Schisturella Norman, Tmetonyx 

 Stebbing,* ^''TryplioscC auct.* { = TryplioseUa Bonnier), Trypliosites 

 Sars, Urisfc.s Dana.* 



The hippomedon group may be divided into two sections, the first, 

 with Hippomedon as representative, having the mandibular molar 

 ridged and cuspidate but never covered with minute setules ; the second, 

 with ^^Tryphosa'''' as representative, having the mandibular molar es- 

 sentially unridged but covered with minute scales or setules and thus 

 appearing fuzzy, the shape of the molar often departing from the 

 orthodox cuboidal shape by slight asymmetrical extension and attenua- 

 tion but never becoming conical or laminate. *Genera of section 2 

 are marked with asterisks in the preceding list. Tryphosites is inter- 

 mediate between the two sections. 



Section 1. — Most of the deep-sea species of questionable classifica- 

 tion belong with the hippomedon section of genera. They have asctu- 

 lose mandibular molars that are often almost completely unridged. 

 They are Paracentromedon crenulafvs (Chevreux), P. carahicus J. L. 

 Barnard, Elimedon cristatus J. L. Barnard, Schisturella rohusta 

 (J. L. Barnard) (described in Amhaslopsls) ^ Pseudonesimus dbyssi 

 Chevreux, Lahota adversicola K. H. Barnard (also assigned to 

 Chironesimus), and Lahota rotundatus K. H. Barnard (also assigned 

 to Chironesimus) , and several new species described herein. They and 

 the types of various hippomedon-like genera are arranged in table 1 

 in relation to several morphological characters. The order in which 

 the characters is arranged is a judgment of their classificatory impor- 

 tance. To illustrate the generic value of characters, one might com- 

 mence with those of least importance to the right of table 1 : (i) the 

 tooth of the third pleonal epimeron in Lysianassidae is highly varia- 

 ble, although Gurjanova (1962) cites it as a diagnostic character of 

 Hippomedon; (h) some characteristics of gnathopod 1 are diagnostic 

 for some genera in the Lysianassidae (viz. scopelocheiras, Op)isa 

 Boeck, Trischizostoma Boeck) ; for instance, the alternatives among 

 simple, subchelate and chelate gnathopods often are of classificatory 

 value but in the group of species assembled in table 1 the state of the 

 palm probably has no generic meaning even though some of the species 



*See text to follow. 



