NO. 1 1 GARTH : DISTRIBUTION STUDIES OF ERACHYURA 609 



the Pacific for the first time by Hancock Expeditions. The remaining 

 four, Cycloes bairdii, Acanthonyx petiverii, Cronius ruber, and (tenta- 

 tively) Tetraxanthus rathbunae, are free living species representing as 

 many different families and about them no generalization seems possible. 



Galapagos species enjoying the greatest latitudinal range are closely 

 restricted to American shores. Mursia gaudichaudii, an oxystome, occurs 

 from the Farallone Islands, off San Francisco, to Valparaiso, Chile. 

 Drorjiidia larrabiirei ranges north to Monterey Bay, while Stenorynchus 

 debilis is found from Magdalena Bay, Lower California, to Chile. All 

 are dredged species and each is the sole representative of its genus in the 

 Eastern Pacific. Usually several species of a genus replace each other 

 along such a continuous coast line. When the break between species 

 occurs with consistent regularity in a number of genera and families it 

 becomes possible to delimit regions each of which supports a characteristic 

 aggregation of brachyuran species. Several such faunal provinces will be 

 mentioned in the discussion which follows. 



The largest number of Galapagos brachyuran species common to any 

 continuous portion of the adjacent mainland are the 48 species which 

 occur from the Gulf of California to southern Ecuador or northern Peru. 

 If to these be added the 15 species common to the Galapagos and the Bay 

 of Panama alone, the total of 63 species gives the Galapagos brachyuran 

 fauna the unmistakable stamp of the Panamic province. It also indicates 

 the predominating influence of the warm Nino Current which emanates 

 from the Bay of Panama from January to April and which may have 

 served to transport larval stages to Galapagan shores. 



The eleven species common to the Galapagos and the Gulf of California 

 — Lower California region but not recorded from the Central American 

 coast are evidence of the infiltration of a north temperate fauna. 

 Microphrys triangulatus may be taken as an example of a Gulf of Cali- 

 fornia species not represented in the Bay of Panama (except at Cocos 

 Island) but well established in the Galapagos. The fact that other 

 Galapagos species are common to the intermediate outposts of Clarion or 

 Socorro {Ebalia hancocki, Clythrocerus laminatus, and Leptodius 

 cooksoni) suggests that these islands, along with Cocos and perhaps 

 Clipperton, Chart IV, may have served as stepping stones for current- 

 borne larval stages. The California Current and Equatorial Counter- 

 current would appear to supply the needed transportation. 



Of the nine species listed as common to the Galapagos and the Sub- 

 antarctic faunal region alone, the Peruvian or Chilean records in four 

 cases rest upon century-old reports which have not been recently verified. 

 Apart from these doubtful records, Mithrax bellii, M. nodosus, Leptodius 



