MARINE GAMMARIDEAN AMPHIPODA 



199 



Description. — Rostrum inconspicuous; accessory flageJlum absent; 

 body smooth or witli slight dorsal teeth; coxa 1 small, hidden by follow- 

 ing coxae; coxa 4 large, either shield-like or excavate posteriorly; 

 upper lip incised; mandible with weak, sparsely spinose molar, not 

 triturative, palp long, 3-articulate; lower lip with coalesced inner 

 lobes, outer lobes with blunt extremities; palp of maxilla 1 uniartic- 

 ulate; maxilla 2 small, lobes blunt; maxillipeds slender, outer lobes 

 vestigial; gnathopods small, first simple, second subchelate; uropod 3 

 uniramous, the single ramus 2-articulate; telson of medium length, 

 entire, fused with pleonite 6; article 2 of pereopod 3 expanded. 



Figure 82. — Cressidae: a, Cressina monocuspis Stephensen (1931); b, uropod 3 of Cressa 

 minuta Boeck (Sars, 1895, pi. 99); c, pleonite 3 and urosome, left to right, of Cressina, 

 showing absence of urosomite 3. 



Relationship. — The Stenothoidae have all segments of the urosome 

 and the telson distinct, coxa 4 is always shield-like, not excavate 

 posteriorly (like Cressina, however) and article 2 of pereopod 3 is 

 always linear. 



All Thaumatelsonidae have coxa 4 shield-like, not excavate pos- 

 teriorly. Although the segments of the urosome may be coalesced the 

 telson is not clearly fused with them and is usually thickened dorso- 

 ventrally; article 2 of pereopod 3 is always linear. 



The Phliantidae have depressed, rugose bodies, and relatively equal 

 coxae. 



