DISTRIBUTION STUDIES OF GALAPAGOS BRACHYURA 



(Charts 1-10) 



By John S. Garth 



PRELIMINARY STATEMENT 



The Galapagos littoral is now credited with supporting some 120 

 brachyuran species, 47 of these by virtue of intensive carcinological col- 

 lecting carried on by Allan Hancock Expeditions in the years 1933-35 and 

 1938 (cf. Sivertsen, 1933). In the course of routine taxonomic studies 

 on Hancock collections which culminated in the writing of the Littoral 

 Brachyuran Fauna of the Galapagos Archipelago (Garth, 1946), 15 

 species were described as new to science (Rathbun, 1933, 1935; Garth, 

 1939; and Glassell, 1940). Several of these were noted as having close 

 trans-Pacific affinities, while the remaining 32 new to the islands repre- 

 sented extensions of range of known species from the North and South 

 American mainland. 



Many species known previously to occur at one or two localities within 

 the islands were found to occur at most of the eleven major and numerous 

 minor islands which comprise the Galapagos group. Others were notice- 

 ably absent over large areas in which their existence might reasonably have 

 been expected. These new data appeared to furnish the basis for an 

 analysis of the distribution of species and genera with a view of ascertain- 

 ing the possible routes by which they arrived in and were distributed 

 through the archipelago. 



INTRA-INSULAR DISTRIBUTION 

 (Charts I-III) 

 The first step in the study was to plot on charts of the Galapagos 

 Islands the stations at which individual species were encountered by Allan 

 Hancock Expeditions. These charts, too numerous for reproduction here- 

 with, are available at the Library of The University of Southern Cali- 

 fornia, where they form a part of the writer's doctoral dissertation. From 

 them it was apparent that the large majority of species were more or less 

 uniformly distributed throughout the length and breadth of the archi- 

 pelago. When the relationships of these species were examined, they were 

 found to be either endemic species, or if non-endemic, species common to 

 tropical faunas : the Caribbean, the Panamic, and the Indo-Pacific. Two 



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