DECAPOD CRUSTACEANS OF THE WEST INDIES 25 



ancestors of the other species. With the more primitive species oc- 

 cm"ring on Isla de Pinos and Cuba, the precursors of the modern 

 members of the genus might well have arrived in the islands about 

 the time that the crayfishes reached them. 



The more advanced Pseudothelphusa is represented in the AntUles 

 by only three species, P. affinis, P. americana, and P. terrestris, of 

 which only the former is an endemic, known only from Cuba. The 

 latter two also occur in the Central American-Mexican region, and 

 P. americana has been found on Puerto Rico. Little is known about 

 these three crabs; it is not even known whether or not they occur 

 sympatricaUy on Cuba, and their phylogenetic and ecological re- 

 lationships are quite obscure. Such evidence as exists, however, points 

 to a Central American-Mexican origin. The remaining members of 

 the genus occur in Colombia, Costa Rica, and southern Mexico. 



In contrast, the two representatives of the genus Guinotia in the 

 West Indies have had a South American origin. Guinotia g. garmani 

 occurs in eastern Venezuela, on Trinidad, and on Isla de Margarita. 

 Almost certainly, the ancestral stock of G. dentata invaded the Lesser 

 Antillean Chain from South America and is now represented by this 

 single species on Guadeloupe, Dominica, Martinique, and Saint Lucia. 

 The remaining species belonging to this genus are endemic to South 

 America. 



The Trichodactylidae : This primarily South American family 

 barely reaches the West Indies in Trinidad, where it is represented 

 by Trichodactylus dentatus, a species with an extensive range in north- 

 eastern South America. A few representatives of the genus in Central 

 America and Mexico have very probably been derived from South 

 American ancestors. Inasmuch as the West Indian examples are con- 

 specific with South American ones, it seems probable that the invasion 

 of Trinidad was comparatively recent. 



The Grapsidae: While almost one-fourth of the freshwater and 

 terrestrial decapods in the West Indies are members of this family, 

 only seven of them are endemic to the islands. Typically, the members 

 of this family have marine larvae, but those of a few species have 

 become adapted to fresh water. 



Pachygrapsus corrugatus, a marine species, is known only from New 

 Providence, Cuba, Puerto Rico, and Saint Croix, where its range over- 

 laps that of P. gracilis and P. transversus. Its affinities with these and 

 other members of the genus are not weU understood, and it can only 

 be supposed that its ancestors reached the Greater Antilles rather 

 early and that perhaps competition with other forms occupying 

 similar habitats has prevented it from extending its range to the 

 nearby continental masses and neighboring islands. 



