436 U.S. NATIONAL MUSEUM BULLETIN 271 



slender, first lar2:er than second, and occasionally weakly chelate, 

 article 3 of gnathopod 2 elongate; iiropod 3 with its single ramus 

 longer than the short peduncle; telson entire. 



Relationship. — The Leucothoidae have biramous third uropods. 

 The Lysianassidae have a short peduncle of antenna 1 ^nth article 2 

 much shorter than 1 whereas the Sebidae not only have an elongate 

 peduncle but article 2 is much longer than 1. Few Lysianassidae have 

 a uniramous uropod 3 and when so it is never elongate. 



The Stenothoidae have subchelate gnathopods and coxa 1 is con- 

 cealed by coxa 2, but mouthparts and uropod 3 indicate a close rela- 

 tionship of the two groups. 



Platyischnopus in the Haustoriidae resembles the Sebidae in its 

 subchelate gnathopods but differs from sebids in its biramous third 

 uropods, much larger outer plates of the maxilliped and cleft telson 



Genera of Sebidae 



Seba Bate 



Seba Bate, 1862.— Stebbing, 1906.— K. H. Barnard, 1957. 

 Teraticum Chilton, 1884. 

 Grimaldia Chevreux, 1889. 

 Paravalettia K. H. Barnard, 1916. 



Type-species: jS. mwomwato Bate, 1862 (monotypy). 



Species: 7, probably cosmopoUtan cold-water, littoral to bathyal. 



Stegocephalidae 



Figures 160, 161 



Diagnosis. — Mouthparts projecting in a conical bundle below 

 head; mandible lacking palp and molar; accessory flagellum 1- 

 or 2-articulate ; gnathopods feeble, simple or weakly subchelate. See 

 Amphilochidae, Lysianassidae. 



Description. — Peduncle of antenna 1 short; mouthparts variable; 

 upper lip bilobed, mandible lacking palp and molar, lower lip without 

 inner lobes; palp of maxilla 1 large or small, with one or two articles, 

 maxilla 2 usually with two plates, outer plate occasionally absent, 

 often set on extended base so as to appear geniculate; maxillipedal 

 palj) with three or four articles; gnathopods feeble, simple or scarcely 

 subchelate; coxae quadrate or roimded below, or first three often 

 acuminate below, first four usually forming a continuous shield, 

 coxa 1 never hidden by coxa 2; uropod 3 variable, peduncle long or 

 short, rami long or short; telson short, or medium, entire or cleft. 



