78 BULLETIN 166, UNITED STATES NATIONAL MUSEUM 



afferent branchial orifices are wide openings immediately in front of 

 bases of chelipeds. Chelipeds in adult male often unequal. First 

 and second pairs of ambulatory legs long and usually rather stout. 

 The last two pairs short and rather sHght; they arise much higher 

 than the other legs and have a small hooklike dactylus folding back- 

 ward. The abdomen of the male usually consists of five pieces, the 

 third to fifth segments being fused or partially so; that of the female 

 consists of seven separate segments; the first three segments visible in 

 dorsal view. 



East and west coasts of Middle America, eastern Atlantic and 

 Mediterranean, and Indo-Pacific region. 



KEY TO THE AMERICAN SPECIES OF THE GENUS ETHUSA 



A*. Eyestalks long, extending laterally beyond outer orbital spine. 

 B'. Outer orbital spine directed obliquely forward. 



mascarone americana (p. 78) 

 B^. Outer orbital spine directed longitudinally forward. 



mascarone pananaensis (p. 79) 

 A^. Eyestalks short, not extending beyond outer orbital spine. 

 B'. Branchial regions separated by the cardiac and gastric regions. 

 C. Dactyls of first and second ambulatories flattened above. 

 D'. Carapace as broad as, or broader than long. 



E'. Eyestalks longer than cornea. Appendages of second 

 abdominal segment of male shorter thap those of first 



segment microphthalma (p. 82) 



E^. Eyestalks very short, muph stouter than cornea. Ap- 

 pejidages of second abdominal segment of male longer 



than those of first segment lata (p. 84) 



D^. Carapace longer than broad truncata (p. 85) 



C^. Dactyls of first and second ambulatories not flattened 



tenuipes (p. 87) 

 B^. Branchial regions meeting on median line, separating cardiac 



from gastric region ciliatifrons (p. 88) 



analogous species of ethusa on opposite sides of the continent 



Atlantic Pacific 



mascarone americana (and Pacific). mascarone panamensis. 



microphthalma. lata. 



ETHUSA MASCARONE AMERICANA A. Milne Edwards 



Plate 22, Figure 2; Plate 23, Figure 2 



Ethusa americana A. Milne Edwards, Bull. Mus. Comp. Zool., vol. 8, p. 30, 

 1880 (type localities, West Florida, 13 fathoms, type in M. C. Z., and lat. 

 26° 16' N., 20 fathoms, type in Paris Mus.). — A. Milne Edwards and 

 Bouvier, Mem, Mus. Comp. Zool., vol. 27, p. 67, pi. 13, figs. 1-4, 1902. 



Ethusa mascarone americana Rathbun, Proc. Biol. Soc. Washington, vol. 11, 

 p. 109, 1897; Bull. Lab. Nat. Hist. State Univ. Iowa, vol. 4, p. 293, 1898; 

 Bull, U. S. Fish Comm. for 1900, vol. 20, pt. 2, p. 89, 1901.— Finnegan, 

 Journ. Linn. Soc. London, Zool., vol. 37, p. 615, 1931, 



