364 U.S. NATIONAL MUSEUM BULLETIN 271 



Stephensenia Schellenberg 



Stephensenia Schellenberg, 1928a. 



Type-species: S. haematopus Schellenberg, 1928a (monotypy). 



Upper lip and epistome not differentially produced; mandibular 

 molar large, blunt, palp absent; gnathopod 1 nearly simple, article 

 5 longer than 6; outer ramus of uropod 3 uniarticulate; telson of 

 medium length, deeply cleft. Species: 1, antiboreal, littoral. 



Stomacontion Stebbing 



Stomacontion Stebbing, 1899d; 1906. 



Type-species: Acontiostoma pepinii Stebbing, 1888 (original 

 designation). 



Mouthparts forming conical bundle, styliform; mandibular molar 

 absent, palp attached very proximally; palp of maxilla 1 biarticulate 

 but very small; maxillipedal palp article 4 vestigial; gnathopod 1 

 simple, article 6 longer than 5; coxa 1 projecting over side of the head; 

 uropod 3 uniramous, ramus vestigial; telson short, apically notched. 

 [Based only on type-species.] 



Note : Species assigned to this genus intergrade with Acontiostoma 

 and two of the species have coxa 1 ventrally subcorneal. Stomacontion 

 capense K. H. Barnard (1916) lacks any first maxillary palp and S. 

 insigne K. H. Barnard (1932) has the first maxillary palp 1-articulate 

 but combined mth a vestigial fourth maxillipedal palp article, and 

 these characters obfuscate the generic limits of Acontiostoma and 

 Stomacontion. Both species, however, have a subconical first coxa, 

 perhaps in itself a useful generic or subgeneric character. Species: 

 5, subantarctic, antiboreal, littoral. 



Thoriella Stephensen 



Thoriella Stephensen, 1915. 



Type-species: T. islandica Stephensen, 1915 (original designation). 



Accessory flagellum absent; flagellum of antenna 2 with especially 

 inflated articles; apparently epistome broadly rounded and produced 

 in front of upper lip; mandibular molar obsolete, palp absent; maxil- 

 liped opercular, inner plates apparently large and subrectangular, 

 outer plates narrower and triangular, palp apparently composed of 

 single large opercular article with deep lateral incision [open to dif- 

 ferent interpretation]; gnathopod 1 simple, short; gnathopod 2 simple; 

 coxae small, short, not touching serially, coxa 4 not excavate pos- 

 teriorly; uropod 3 lacking rami; telson absent. Species : 1, N. Atlantic, 

 Indian, abyssopelagic. 



