OXYSTOMATOUS AND ALLIED CRABS OF AMERICA 77 



KEY TO THE AMERICAN GENERA OF THE FAMILY DORIPPIDAE 



A'. The external maxillipeds leave all the anterior part of buccal 

 cavern uncovered. 

 B'. Basal segments of antennules normal. Eyestalks movable, 



directed forward Ethusa (p. 77) 



B2. Basal segments of antennules very large and swollen, crowd- 

 ing eyes and antennae almost transversely. Eyestalks 



immovable Ethusina (p. 89) 



A2. The external maxillipeds are greatly elongate and do not leave 



any appreciable portion of buccal cavern uncovered. 



B*. Carapace quadrate. Rostrum rather narrow, triangular, 



acute at end. Afferent orifices reduced or rudimentary. 



Efferent orifices more or less separate and situated behind 



the front. 



C. Eyes without pigment. Antennules large, unconcealed. 



Merus of outer maxilliped produced forward far beyond 



carpal articulation Cymonomus (p. 96) 



C^. Eyes normally developed. Antennules folding under 

 front. Merus of outer maxilliped not overreaching 



palp Cymopolus (p. 98) 



B^. Carapace oval or subcircular. Rostrum little prominent or 

 divided at end. Efferent orifices contiguous and united in 

 a gutter approaching frontal border; no afferent opening at 

 base of anterior feet. 

 C Carapace transversely oval, branchial regions much dilated 

 in aU directions. Efferent orifices reaching anterior bor- 

 der of front, which is triangular, obtuse. Eyes pig- 

 mented Corycodus (p. 101) 



C^. Carapace subcircular. 



D'. Antennules long, incapable of folding into antennular 



cavity. Antennae with narrow peduncle Cyclodorippe (p. 103) 



D^. Antennules small, completely retractile; antennae very 



short, with valviform peduncle Clythrocerus (p. 109) 



Genus ETHUSA Roux 



Ethusa Roux, Crustac^s de la Mediterranee et de son littoral, p. [81], 1828 (type, 



E. mascarone Roux). 

 Pridope Nardo, Mem. 1st. Veneto, vol. 14, p. 307, 1868 (type, P. typica Nardo). 



Carapace flat, truncate-oblong and broadest behind, covering little 

 more than the first two thoracic sterna; hepatic region small. The 

 front consists of two laminar teeth, each of which is bifid. A tooth or 

 spine at antero-external angle of carapace. The antennules fold 

 obliquely; they are large and project beyond their fossae. The 

 antennae have a long flagellum; their basal article is inserted between 

 the eyestalk and the basal antennular article, but on a slightly lower 

 level. The buccal cavern is elongate-triangular and does not extend 

 to the front; the external maxillipeds cover only its basal three-fourths, 

 but the distal part is closed in by the stout, foliaceous processes of the 

 first maxillipeds. The palp of the external maxilHpeds arises from the 

 summit of the merus and is completely exposed in flexion. The 



