DECAPOD CRUSTACEANS OF THE WEST INDIES 105 



two Oil propodus; dactyl translucent pink with corneous tip. Pleopods 

 translucent pink. 



Female with essentially same coloring and similar basic patterns; 

 however, carapace with three to nine additional dark, irregular spots 

 laterally and dorsolateraUy, chiefly in branchiostegal area. 



Juveniles with coxa and basis of second and third pereiopods deeply 

 pigmented. 



Material examined. — The Dominican collections contain 247 

 males (carapace lengths 2.8-18.2 mm), 294 females (cl 2.8-12.5 mm), 

 including 69 with eggs (cl 5.1-12.5 mm), and 413 juveniles (cl 1.8- 

 3.2 mm). The smallest recognizable males, in which the appendix 

 masculina on the second pleopod is no more than a bud, have cara- 

 pace lengths of 2.8 and 2.9 mm, but that appendix may not be fully 

 developed at a carapace length of 4.6 mm. 



Ecological notes. — Macrobrachium faustinum is primarily an in- 

 habitant of the lower reaches of streams on Dominica, and even here 

 it is much more abundant in the quieter portions of the streams 

 w^here it seeks shelter beneath stones, trunks of water-logged trees 

 that rest submerged on the bottom of the stream bed, palm fronds, 

 and coconut husks that also lie on the bottom of shallow parts of 

 the stream. Seldom does it venture into riffle areas where the water 

 is rushing but it is frequently found close to the shore in such areas 

 if the littoral waters are not swift. 



What these shrimp do during flood stages of the lower portions of 

 the streams, when the latter are converted to torrents, rising some 

 six or eight feet, is not known, but shortly after the river has subsided 

 to its former level, M. faustinum is back in its old haunts. 



At Clarke Hall, this shrimp frequents the lee side of a bend of the 

 Layou River, where coarse sand has accumulated and the bottom 

 gently slopes downward to a depth of some 12 feet, thus providing a 

 splendid beach for swimming and bathing. On a number of occasions, 

 bathers there have been "nipped" on the feet and legs by small in- 

 dividuals of this shrimp. Fortunate for the bathers, the larger in- 

 dividuals are much more retiring. The population on this sand bar is 

 a rather sparse one, but some shrimp are always there, and the place 

 lends itself to making obervations on the shrimp with the use of a 

 face mask. The area close to the shore, and just below the riffles, seems 

 always to be populated by a number of juveniles that actively wander 

 over the bottom with their chelae outstretched, apparently giving 

 consideration to every object that invades the area, whether it be a 

 tiny fragment of a leaf or something as large as the feet and legs of a 

 man. Here on the lee side of the river, a moderately strong eddy current 

 occasionally arrests objects that are comparatively heavy and they 

 become temporarily imbedded in the sand. Almost certainly, it is the 



