172 U.S. NATIONAL AIUSEUM BULLETIN 292 



as carapace, margin with deep median sinus, obscurely quadrilobate 

 in dorsal view. Eyes well developed but rather small, cornea narrower 

 than basal portion of eyestalk. Ventral margin of orbit denticulate, 

 paralleled by longer row of denticles ventral to first, but not sharply 

 produced and not ciu-ving ventrally to anterolateral angle of mouth 

 area. Third maxilHpeds without oblique hauy ridge, narrowly gaping, 

 exposing tips of mandibles. Chelipeds very unequal, carpus unarmed 

 on flexor margin; palm tuberculate dorsally; fmgers of major chela 

 very narrowly spoon tipped, of minor chela broadly spoon tipped, 

 extensor margins of movable fingers tuberculate. Walking legs not 

 broad and flattened, merus of third pereiopod less than one-third as 

 wide as long, with subrectangular subdistal tooth on extensor margin; 

 dactyl slightly shorter than extensor margm of propodus. First pleo- 

 pod of male terminating in posterior view in long chitinous endpiece 

 directed anterolaterally (fig. 52/). A fairly large species, maximum 

 carapace length in midline about 40 mm. 



Habitat. — Fresh water. 



Distribution. — Known only from Jamaica. 



Subfamily Sesarmiimae 

 Genus Aratus 



64. Aratus pisonii (H. Milne Edwards) 



Figures 54, 58a 



Sesarma Pisonii H. Milne Edwards, 1837, p. 76, pi. 19: figs. 4, 5 [type-locality: 



Antilles]. 

 Aratus Pisonii. — 11. Milne Edwards, 1853, p. 187. 

 Aratus pisonii.— Rathhun, 1918, p. 323, pi. 96.— HartnoU, 1965, pp. 115-131, 



140, 141, 143, 144, 145, figs. 1-9, tables 1-5. 



Diagnosis. — Carapace trapezoidal, more than nine-tenths as long 

 in midline as wide (appearing longer than wide), slightly convex 

 longitudinally, markedly so transversely, striations on lateral portions 

 only; lateral margins strongly converging posteriorly, unarmed pos- 

 terior to outer orbital angle, fronto-orbital distance representing 

 maximum width of carapace; front strongly deflexed, about seven- 

 tenths as wide as carapace, margin slanting slightly posteriorly 

 toward midline in dorsal view. Eyes very well developed, cornea 

 wider than eyestalk. Ventral margin of orbit sharply produced, 

 minutely denticulate, curving to anterolateral angle of mouth area. 

 Third maxillipeds with oblique hauy ridge on merus, widely gaping, 

 exposing mandibles. Chehpeds subequal, carpus vhtually unarmed, 

 few denticles on flexor margin; palm sharply tuberculate dorsally; 

 fingers subacutely spoon tipped, extensor margin of movable finger 



