DECAPOD CRUSTACEANS OF THE WEST INDIES 19 



caris and Troglocubanus cannot presently be postulated. The mono- 

 typic Metopaulias is believed to have had a common origin with 

 the freshwater members of the Jamaican representatives of the genus 

 Sesarma, and the stock from which they arose probably reached the 

 island from the Central American-Mexican region. 



The West Indian species. — This discussion is devoted largely to 

 the species that are known only from the West Indies; however, 

 where appropriate, other more widely ranging ones are introduced. 

 For the remaining species, either their ranges are so broad or our 

 data so meager that nothing can be said concerning the migratory 

 routes followed by their ancestors or the relative times of their 

 arrivals. 



The Atyidae: Of the 11 Antillean atyids, 7 are endemic to the 

 islands: Atya lanipes, Jonga serrei, Micratya poeyi, Potimirim ameri- 

 cana, Typhlatya garciai, T. monae, and Xiphocaris elongata. Among 

 them are some of the most generaUzed and some of the most specialized 

 members of the family. Except for the two members of the genus 

 Typhlatya, aU of them probably have larval stages that undergo part 

 of their development in the sea, thus minimizing the possibihty of 

 deciphering their sources of origin. Nevertheless, postulates concerning 

 migratory paths of the ancestors of some of them are presented with 

 some degree of confidence. 



Only one member of the genus Atya is endemic in the West Indies. 

 Atya lanipes, one of the most primitive members of the genus, is 

 confined to the islands of Puerto Rico and Saint Thomas, and its 

 presence in the midst of the ranges of its relatives A. innocous and A. 

 scabra, both of which occur on Puerto Rico, is somewhat surprising. 

 The presumed absence of the latter two on Saint Thomas suggests the 

 possibilities that^. lanipes became differentiated on Saint Thomas and 

 that its presence on Puerto Rico represents a subsequent invasion. 

 Perhaps, however, it had its origin on Puerto Rico and migrated to 

 Saint Thomas, establishing a population there that has succeeded in 

 warding off the subsequent invasions of A. innocous and A. scabra, 

 a feat that it was not able to accomplish on the larger island of Puerto 

 Rico. Little is known of the habits of this species; thus, an evaluation 

 of its probable fate on Peurto Rico cannot be judged. 



A lack of knowledge that would permit a postulate as to the range 

 of the primeval Atya stock with its presumed marine larvae almost 

 obviates speculation concerning the origins of the three West Indian 

 species. It seems highly unlikely that the primitive A. lanipes is 

 presently occupying the original home of the genus. Suffice it to 

 say that A. lanipes is the most primitive of the three, A. scabra the 

 most advanced, and that A. innocous is somewhat more primitive 

 than the latter. 



