200 U.S. NATIONAL MUSEUM BULLETIN 271 



Key to the Genera of Cressidae 



1. Coxa 4 rectangular, excavate posteriorly (fig. 81a) Cressa 



Coxa 4 shield-like, not excavate posteriorly (fig. 82a) Cressina 



Genera of Cressidae 



Cressa Boeck 



Danaia Bate, 1857a (homonym, Anthozoa). 

 Cressa Boeck, 1871.— Stebbing, 1906. 



Type-species: Danaia dubia Bate, 1857a (selected by Boeck, 1876, 

 as Cressa schiodtei Boeck, 1871). See Sars, 1895. 



Species: 6, arctic-boreal, N. Atlantic, littoral to bathyal. 



Cressina Stephensen 



Cressina Stephensen, 1931. 



Type-species: C. monocuspis Stephensen, 1931 (monotypy). 

 Species: 1, subarctic, bathyal (682-1,096 m). 



Dexaminidae 



[including Anatylidae Bulycheva, 1955] 



Figures 83-85 



Diagnosis. — Accessory flageUum absent; urosomites 2 and 3 

 coalesced; mandible lacking palp, molar well developed or vestigial; 

 uropod 3 biramous; telson deeply cleft; body laterally compressed; 

 gnathopods feeble but subchelate. See Atylidae, Prophliantidae, Phlian- 

 tidae. See Sphaerophthalmus in "Incertae Sedis." 



Description. — Accessory flagellum absent; body laterally com- 

 pressed and often dorsaUy carinate or toothed; urosomites 2 and 3 

 coalesced; mandible lacking palp, molar well developed, triturative 

 (Dexamininae) or evanescent (Anatylinae) ; lower lip with or without 

 mandibular processes, inner lobes well developed or vestigial, occa- 

 sionally fused ; palp of maxilla 1 uni- or biarticulate ; maxillipeds with 

 3- or 4-articulate palp, inner plates occasionally vestigial ; gnathopods 

 feeble, subchelate; pereopods occasionally cheliform; lu^opod 3 

 biramous; telson long or short, deeply cleft. 



Relationship. — The Talitroidea have fully separated urosomal 

 segments. 



Phliantidae and Prophliantidae have the mandibular molar evanes- 

 cent. The Phliantidae, furthermore, have the palp of maxilla 1 de- 

 graded or absent. The Prophliantidae have all urosomal segments 

 coalesced. 



