DECAPOD CRUSTACEANS OF THE WEST INDIES 39 



large individuals frequently wander some distance from their lairs. 

 At Tarou Cliffs (pi. 3b), numbers of young Cardisoma and Gecarcinus 

 lateralis were found in shallow "dry" burrows along the shaded, 

 northern talus slope. The three species of the genus Gecarcinus usually 

 seek higher ground than does C. guanhumi but apparently do not 

 travel as far inland as Coenohita. During the breeding season, they 

 often move in large groups toward the sea. 



One of the most unusual decapods in the Antilles is the endemic 

 Cuban Barbouria cubensis, which frequents landlocked brackish or 

 salt water pools. 



It is obvious from the foregoing discussion that little is known 

 of the habits and life histories of most of the freshwater and terrestrial 

 decapods of the West Indies. Except for the careful studies of Hartnoll 

 (1964 and 1965), Laessle (1961), and the limited observations made 

 on the Dominican fauna recorded herein, all data are exceedingly 

 cursory. 



On Dominica (and, we suspect, on most of the smaller islands of 

 the Antilles), ecological factors seem to have played a far more 

 important role in the distribution of its decapod fauna than has 

 topography. There, whether on the windward or the leeward slopes, 

 where a particular type of habitat exists, the same assemblage of 

 decapods was found to be present. (For example, all of the typically 

 freshwater decapods reported from the island occur in the Layou 

 River System.) Whereas on most continental land masses and on 

 many larger islands species are limited in their distribution by physical 

 barriers of one sort or another, this does not appear evident on 

 Dominica. Despite the rugged topography, the numerous (at least 

 365) streams that have cut deep valleys and the relatively xeric 

 habitats that separate the lower portions of some of the streams, 

 barriers to the decapods if they ever existed, are no longer effective. 

 A number of factors have made possible the crossing of potential 

 barriers by all of the decapods present on the island : 



1. In the sense that terrestrial organisms are not dependent on 

 water except that taken internally, truly terrestrial decapods do 

 not exist; all of them must have at least a film of water covering their 

 branchial siu-faces, and this water is acquired directly from the 

 environment. In an atmosphere of such high humidity as that on 

 Dominica, enhanced by frequent precipitation, such decapods as 

 Coenobita clypeatus and the two species of the genus Gecarcinus 

 can exist for weeks or months without having to return to standing 

 water. Furthermore, while they are not characteristically found in 

 bodies of fresh water, such streams as do exist on Dominica woidd 

 hardly present a formidable barrier to them. Inasmuch as the so-called 

 terrestrial crabs have marine larval stages, even if the lower reaches 



