NO. 3538 DECAPOD CRUSTACEANS — CHACE 655 



Africa to St. Helena in the trade-wind drift; this explanation almost 

 certainly applies to Planes, which is a habitual passenger on floating 

 weed. Calappa gallus, which occasionally occurs on the east coast of 

 South Africa, probably never reaches the Cape of Good Hope, and 

 there is Uttle likelihood that it migrated directly from there to St. 

 Helena in the recent past. The evidence of a link between the faunas 

 of St. Helena and South Africa is even more obscure in the mollusks, 

 of which only 6 of 182 St. Helena species were known from South 

 Africa, but Cunningham reported a closer relationship in the fishes, 

 of which no less than 12 of 33 St. Helena species were reported from 

 South Africa. 



One of the more surprising disclosures of the study of the Loveridge 

 collections is the number of Pacific species represented. The propor- 

 tion of decapods common to St. Helena and to the Indo-Pacific (30 

 percent) and eastern Pacific (26 percent) is noticeably greater than it 

 is in the fishes (24 and 18 percent), mollusks (8 and 5 percent), and 

 echinoderms (15 and 8 percent). Also, at least four of the decapods 

 that have been reported from the Pacific {Alpheus paragracilis, En~ 

 oplometopus antillensis, Micropanope melanodactylus, and Planes 

 marinus) seem to have discontinuous distributions. (The probable 

 occiu-rence of Planes cyaneus off South Africa eliminates that crab 

 from this group.) A possible explanation for such interrupted dis- 

 tributional patterns (aside from insufficient collecting) is that some 

 of the species have been transported on the hulls of ships. For those 

 species that could withstand a few days' exposure to cool tempera- 

 tiu-es, there was ample opportunity for introduction to St. Helena by 

 this method when the island was a regular port of call for vessels 

 sailing around Cape Horn or the Cape of Good Hope before the 

 construction of the Suez and Panama Canals. 



Finally, the four possibly edemic decapods thus far described from 

 St. Helena (JDardanus imperator, Pachygrapsus loveridgei, Acanthonyx 

 sanctaehelenae, and Pisa sanctaehelenae) are proportionately fewer (17 

 percent) than are the fishes (29 percent), mollusks (52 percent), and 

 echinoderms (50 percent) that are confined to St. Helena (and Ascen- 

 sion Island). Further collecting, or even the study of existing col- 

 lections, may reveal additional undescribed species, and it is not 

 unlikely that specimens now assigned to some of the more widely 

 ranging species, such as Pontonia pinnophylax, Alpheus macrocheles, 

 Panulirus echinatus, Enoplometopus antillensis, Dardanus arrosor, 

 Alhunea carabus, and Dromia erythropus, will eventually prove to be 

 specifically or subspecifically distinct. 



