194 U.S. NATIONAL MUSEUM BULLETIN 292 



white; latter wdth narrow purple bands at articulations of basal three 

 segments and at base of telson. 



Material examined. — -The Dominican collections contain only 1 

 male (carapace length 30.9 mm) and 2 females (cl 19.6 and 28.5 mm), 

 the larger of which is ovigerous. The smaller female has the abdomen 

 rounded but not fully formed. 



Ecological notes. — Plagusia depressa is a marine crab that is 

 frequently found clinging to rocks at tide level. It was observed at 

 only one locality on Dominica. At the mouth of the Indian River at 

 Portsmouth, a concrete retaining wall has been built to help preserve 

 the depth of the channel. On the south wall, cracks have developed 

 along the water line, and this crab has apparently found a congenial 

 niche in these fissures that presumably lead back into interstices 

 among the rock fill. The three specimens were collected from the 

 surface of the shady wall, where they were in company with Grapsus 

 grapsus, which showed no preference for shade. When pursued, most 

 Plagusia sought refuge in the fissures and did not reappear. 



Distribution. — North Carolina to Estado de Pernambuco, Brazil 

 (Bermudas, Great Abaco I., Eleuthera I., New Providence I., Cuba, 

 Jamaica, Hispaniola, Puerto Rico, Saint Thomas, Saint Croix, 

 Dominica, Martinique, Barbados, Trinidad, Curasao); eastern 

 Atlantic from Mauritania to northern Angola. 



Dominica Station: 113. 



Remarks. — All three Dominican specimens were taken at the same 

 time, on March 9, 1966. On the day following, not an individual of the 

 species could be found, and subsequent visits by other collectors also 

 proved futile. 



Family Gecarcinidae 



Key to the Species 



1. Dactyls of walking legs armed with four rows of spines 2 



Dactyls of walking legs armed with six rows of spines 3 



2. Fronto-orbital distance nearly or more than two-thirds of carapace width in 



adults; third maxillipeds with exopod and palp well developed and exposed 



to view Cardisoma guanhumi (p. 195) 



Fronto-orbital distance about half of carapace width in adults; third maxilli- 

 peds with exopod and palp reduced and concealed from view. 



Gecarcinus lateralis (p. 198) 



3. IMerus of third maxilliped with notch on mesial margin leading inward to 



closed fissure Gecarcinus lagostoma (p. 197) 



Mcrus of third maxilliped without marginal notch or fissure. 



Gecarcinus ruricola (p. 200) 



