342 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 5 



occidentalis (Faxon), dredged in over 300 fathoms; T r achy car cinus 

 corallinus Faxon, dredged in over 600 fathoms; and Ethiisina gracilipes 

 Miers, dredged in over 800 fathoms, all by the Albatross (Rathbun, 1898, 

 1907; Faxon, 1893, 1895). 



It is intended that the study be used in connection with the Rathbun 

 monographs (Grapsoid, 1918; Spider, 1925; Cancroid, 1930; and Oxy- 

 stome, 1937), to which it is assumed each worker will take recourse for 

 full descriptions of families, genera, and previously known species. How- 

 ever, the introduction of two genera new to the Americas in the writer's 

 Neiu Brachyuran Crabs from the Galapagos Islands (1939) calls for the 

 inclusion of their descriptions, which occur in scattered or generally un- 

 available publications rather than in the above accessible works. Simplified 

 keys to species, sufficient only to distinguish known Galapagos congeners 

 one from another, are introduced whenever two or more species of a 

 genus are represented in the insular fauna. Keys to genera are not given, 

 since they would be nearly as extensive as the Rathbun keys and should, 

 in the opinion of the writer, be reserved for similar monographic reports. 



References to literature have of necessity been limited to the original 

 description, the first use of the name in its current combination, and the 

 citation placing the organism in the Galapagos fauna, if not included in 

 the above two. In cases of involved synonymy, the reader is referred to 

 the appropriate Rathbun monograph; citations of the occurrence of the 

 species in the Eastern Pacific subsequent to the publication dates of the 

 respective monographs are, however, given in full. 



The inconvenience experienced by Velero III workers in attempting 

 to use lengthy descriptions under field conditions has resulted in the sub- 

 stitution of brief diagnoses of the outstanding characters of each species 

 as observable without microscopic examination. These, with the aid of 

 the keys and illustrations given, should enable the field collector to 

 identify his specimens quickly and accurately, a task in which he will be 

 greatly assisted by Mr. Anker Petersen's notes on living specimens based 

 on Ridgway, Color Standards and Color Nomenclature (1912). 



Since the publication in the Rathbun monograph (1937) of the oxy- 

 stomatous and allied crabs taken on the Hancock Expeditions of 1933-34, 

 approximately one half of the specimens so recorded have been returned 

 by the U. S. National Museum to the Allan Hancock Foundation, and 

 it has been possible to list such specimens herein, as well as to enumerate 

 for the first time the oxystomes obtained on the 1935 and 1938 cruises. 

 Subsequent to the publication of this paper a similar division of the non- 

 oxystomatous crabs will be worked out, approximately one half of the 

 specimens of each species to be returned by the Allan Hancock Foundation 



