106 U.S. NATIONAL MUSEUM BULLETIN 292 



eddy current that makes the sandy area so attractive to the M. 

 iaustinum population, and as temporarily anchored as these broken 

 limbs, portions of palm fronds, or coconut husks may be, adult in- 

 dividuals of this shrimp are always present among the debris. Without 

 a face mask to ascertain where the disturbed shrimp are wandering or 

 swimming, the observer finds catching them in open water to be some- 

 what difficult. The shrimp are so palely translucent they are almost 

 indistinguishable from the underlying sand. At night, when all of the 

 shrimp venture from their lairs, the ruby-colored light reflected from 

 their eyes when a beam of light is trained upon them renders the 

 animals utterly conspicuous. 



This species apparently never ascends cascades and has been taken 

 consistently at comparatively low elevations (mostly under 200 feet, 

 but up to 400 feet) where the gradient of the stream bed is quite low. 



Distribution. — West Indies (Andros I., Cuba, Jamaica, Hispaniola, 

 Puerto Rico, Saint Thomas, Saint Croix, Dominica, Saint Lucia I., 

 Saint Vincent, Barbados, Grenada, Tobago, Bonaire, Curasao). 



Dominica Stations: 1, 2, 10-12, 14, 15, 17, 21, 22, 24, 25, 28, 30, 

 32, 33, 36, 37, 40, 42, 49, 52, 54, 56, 57, 59, 61, 63, 67, 68, 71, 72, 75, 

 77, 79-81, 85-88, 95, 100, 102 (0-400 ft.). 



Remarks. — Macrobrachium faustinum is a higlily variable species. 

 For some time, it appeared that two species were among the Dominican 

 specimens that were being assigned to it. One of them is drab buff in 

 color with the carpus of the major chela shorter than the merus and 

 the chela comparatively heavy; the other is darker, with prominent 

 bands on the legs, the carpus of the second pereiopod longer than the 

 merus, and the chela quite slender. When series of the two are com- 

 pared, however, it appears that the combinations of characters are 

 not consistent, and at least some of the differences in color are due to 

 adaptations to light and dark backgrounds. The relative lengths of 

 the carpus and merus of the second pereiopods cannot be correlated 

 with any of the other differences, and in some specimens their lengths 

 are subequal. 



Ovigerous females were collected in January, February, March, 

 April, July, and October, suggesting that this species may breed 

 throughout the year. In the first four months, the only period during 

 which significant numbers of specimens were collected, about 40 per- 

 cent of the females with carapace lengths of more than 5 mm have 

 eggs. 



21. Macrobrachium heterochirus (Wiegmann) 



FiGUBES 24, 25e, k 



Palaemon heterochirus Wiegmann, 1836, p. 149 [type-locality: "east coast of 

 Mexico"]. 



