148 Bulletin, Vanderhilt Marine Museum, Vol. Ill 



The third, fourth and fifth pairs of legs are similar, subequal, 



fairly stout and with the dactyl short, acuminate. 



Synonymy. — Cancer (Astacus) jamaicensis Herbst, Naturg. Krabben 

 u. Krebse, vol. 2, p. 57, pi. 27, fig. 2, 1792. 



Palaemon jamaicensis H. Milne Edwards, Hist. Nat. Crust. II, p. 

 398, 1837.— Ortmann, Zool. Jahrb., vol. 5, p. 729, pi. 47, fig. 7, 

 1891. — MoREiRA, Archiv. Mus. Nac, Eio de Janeiro, vol. II, pp. 13, 

 78, 1901. — Boone, Bull. Bingham Oceanog. Coll., vol. 1, art. 2, 

 p. 112, 1927. 



Bithynis jamaicensis Pocock, Ann, Mag. Nat. Hist. (6), vol. 3, p. 10, 

 1889.— Rathbun, Bui. U. S. Fish. Comm., vol. 20, part 2, p. 123, 

 1900 (1901). 



Macrohrachium jamaicense Rathbun, Proe. U. S. Nat. Mus., vol. 38, 

 p. 561, pi. 51, fig. 1, 1910. — ScHMiTT, Zoologiea, N. Y. Zool. Soc, 

 vol. 5, No. 15, p. 169, 1924 ; Bull. Amer. Mus. Nat. Hist., vol. 53, 

 pp. 37-39, 1926. (Discusses the separation of the African species 

 long confused with M. jamaicense by various authors.) 



Family: PONTONIDAE. 

 Genus : PONTONIA Latreille. 

 Pontonia margarita S. I. Smith. 



Plate 52. 



Type: From the Bay of Panama, in pearl oysters; depository not 

 cited. 



Distribution : Costa Rica to Panama, in Margaritiphora fimbriata 

 and Pinna sp. 



Material examined : Two specimens taken at Punta Arenas, Costa 

 Rica, February, 1928, by the ''Ara." 



Technical description: Carapace is 15 mm. long, including the 

 rostrum, which is 3.6 mm. from tip to orbital angle, a slender acumi- 

 nate triangle, with the dorsal surface flat, glabrous. The rostrum 

 extends as far forward as the distal end of the second peduncular 

 articles of the antennulae. The carapace is four-fifths as wide as long, 

 glabrous, with a slender, acute, branchiostegal spine which is about 

 as long as the basal antennal article. The abdominal segments in the 

 female are broad, with well-developed, rounded epimeral plates, except 

 the sixth segment, which is produced into a narrow, triangulate pro- 

 jection, one on each side at the base of the telson, which is about one 

 and one-half times as long as the sixth segment, narrow, tapered, the 



