DECAPOD CRUSTACEANS OF THE WEST INDIES 31 



While there is no concrete evidence that any stock, once reaching 

 the islands, has reinvaded the neighboring continental masses, it is 

 tempting to postidate that the gecarcinids, and perhaps other groups, 

 reached southern Florida from the Antilles or Bahamas, and it is 

 not unthinkable that some few, the origins of which are highly- 

 problematical, may well have moved in the opposite direction. 



It is a necessary assumption that there has been a considerable 

 amount of "island hopping" once a stock became established in the 

 West Indies, but here again, data are few that permit ascertaining 

 which island or island groups were first invaded; consequently, the 

 directions of migrations are most often undecipherable. 



Almost certainly Cuba has served as the center of dispersal for 

 the genus Epilobocera, from which the ancestral stock spread to 

 Hispaniola, Puerto Rico, and Saint Croix. Cuba may well have served 

 also as the primary insular home of the stock from which Troglocubanus 

 was derived, but it is not inconceivable that the stock reaching 

 Jamaica might have arrived first and subsequently spread to Cuba 

 with the more primitive facies being preserved in southern Cuba. 

 The ancestral stock of Typhlatya monae also very probably reached 

 Isla Mona (Puerto Rico) from Cuba. Guinotia dentata, Potimirim 

 glabra, and Trichodactylus dentatus, all tliree having South American 

 ancestries, are the only decapods that can be said with little doubt 

 to have moved northward in the Lesser Antillean chain. 



One can scarcely resist posing the question as to why the cray- 

 fishes, as successful as they have been on Cuba, have not spread 

 further through the Antilles. Inasmuch as the freshwater crab and 

 shrimp faunas on Cuba are no poorer than on the remaining islands 

 of the Greater Antilles, one might expect the crayfishes to have been 

 equally successful on these islands. The obvious answer is that a 

 crayfish stock just never got there, or, if it did, the arrival was too 

 late to establish niches in the freshwater habitats before they were 

 occupied by other decapods. One also wonders, with the compara- 

 tively rich freshwater grapsid (Metopaulias and Sesarma) fauna on 

 Jamaica, why they too have not spread to the other islands. Can it 

 be, as Hartnoll has suggested, that the absence of other freshwater 

 crabs on Jamaica has made possible the adaptive radiation occurring 

 in this family? From the standpoint of decapods at least, the bro- 

 meliads on all of the islands bear a vacuum awaiting the invasion 

 of a Metopaulias-like crab ! 



The follomng tabulations are presented as summaries that may 

 be of interest to students of zoogeography who are concerned with 

 the Antillean Region. 



The numbers of taxa of freshwater and terrestrial decapods, excluding 

 primarily marine forms (see footnotes), occurring on some of the West 



