186 U.S. NATIONAL MUSEUM BULLETIN 292 



mm). Associated with the smallest specimen, which may represent 

 the first crab instar, were 10 megalops (cl 1.1 mm), apparently be- 

 longing to this species. Vestigial first pleopods were noted in males 

 ranging in carapace length from 3.2 to 3.8 mm. Females wuth a cara- 

 pace length of about 11 mm have the abdomen broadly rounded 

 but not quite fully developed. 



Ecological notes. — This is one of the commonest semiterrestrial 

 crabs on Dominica, occurring in seepage areas and along streams to 

 an elevation of about 1,000 feet, but it is much more frequently seen 

 at lower elevations. Along small streams (pi. 1) such as Mannet's 

 Gutter, it crawls over the surface of exposed rocks both in the stream 

 and along the banks; if pursued, it retreats into the water as readily 

 as it seeks concealment under stones. The orange and purple chelae 

 and the green eyes make it conspicuous in any of the surroundings 

 where it has been observed. 



Large numbers of this crab occur between the upper bridge across 

 the Layou River and the warm spring, some 100 yards upstream, 

 along the foot of the adjacent cliff. In this area there are several 

 seepages along the face of the cliff, and in some places larger elements 

 of the rubble from the cliff have partially blocked the current along 

 the shore. In these seepage areas and among the rubble, this crab 

 occurs in numbers. During light rains, dozens of them have been 

 seen moving along the almost vertical surface of the cement retain- 

 ing wall at the west end of the bridge, and on several occasions 

 crabs escaped being captured by scaling the wall of the cliff. While 

 individuals have not been seen in the direct sunlight, they are by 

 no means strictly nocturnal for they are active in slightly shady 

 areas at noon on the brightest day. 



In contrast to the restrictions that appear to limit the range of 

 this crab on Jamaica (Hartnoll, 1965) to the vicinity of brackish 

 water, on Dominica S. roberti is equally as abundant in and along the 

 shores of freshwater streams for some distance inland. Numbers of 

 ovigerous females were observed at least a mile and a half upstream 

 from the mouth of the Layou River. Even though this is one of the 

 few streams on the island in which an estuarine habitat exists at 

 any time, it is unlikely that brackish conditions ever extend more 

 than 200 yards upstream from the mouth, even temporarily during 

 the highest tides. 



Distribution. — West Indies, Veracruz, Mexico, to San Juan del 

 Norte, Nicaragua; Venezuela (Cuba, Jamaica, Hispaniola, Puerto 

 Rico, Saint Thomas, Saint Croix, Dominica, Martinique, Saint Lucia 

 L, Barbados, Trinidad). It seems verj'- unlikely, as pointed out hj 

 Monod (1956), that *S. roberti occurs in West Africa, especially on 

 Gor^e Island, the indicated type-locality of the species. 



