342 OKTMANN— DISTRIBUTION OF DECAPODS [April * P 



genus Epilobocera (from Cuba to Porto Rico and Sta. Cruz) are 

 restricted to these islands and do not possess any closely allied 

 forms on the mainland, although there is no doubt that they are 

 distantly related to the Central and South American freshwater 

 crabs and must have been derived from these parts. Thus it seems 

 that we are to distinguish two groups among the freshwater Crusta- 

 ceans of the Greater Antilles, pointing to two migrations from the 

 mainland of Central America — an older one, represented by 

 Epilobocera, the higher age of which is supported by the fact that 

 this genus possesses in some respects the most primitive characters 

 among the whole subfamily, and a younger migration, represented 

 by the identical species of Pseudothelphusa. It is doubtful to 

 which of these groups Cambams cubensis belongs, since it is differ- 

 ent from but closely allied to a Mexican species. 



Entirely different in its relations is the Pseudothelphusa (P. 

 dentata) of the Lesser Antilles. This one points beyond doubt to 

 South America (Trinidad and Venezuela) and bears no relation at 

 all to the Greater Antilles, not to speak of Mexico. 



The geology and tectonics of the West Indies and Central 

 America are only poorly known, but lately some very important 

 contributions have been published. Nevertheless, the conditions 

 prevailing here are far from being clear, and the opinions of differ- 

 ent authors vary frequently. This much seems to be sure, that the 

 history of this section of the earth is a very varied and complex one. 



In the first line we are to consider the fact that the general feat- 

 ures of the main mountain ranges of Central America and the West 

 Indies possess much in common and differ sharply from both North 

 and South America. Especially the west-easterly strike of the old 

 ranges of Central America (Guatemala, Honduras), as well as of 

 the Greater Antilles (Cuba, Hayti, Porto Rico, Jamaica), is very 

 remarkable (see Suess, 1885, p. 698 ff.), and indicates a former 

 tectonic unit. According to Hill (1898), old rocks exhibiting the 

 same west-easterly strike are found largely distributed also in Nica- 

 ragua and Costa Rica, and, further, in the region of the Isthmus of 

 Panama, especially to the east of Colon, in the Cordilleras of San 

 Bias. Furthermore, the whole northern shore of Venezuela, from 

 Puerto Cabello to the northeastern end of the island of Trinidad, 

 consists of old granitic ranges with the same strike. All these obser- 

 vations, although apparently incomplete and scattered, most likely 



