1890.] NATIRAL SCIENCES OE PHILADELPHIA. .335 



Echiiiodeniis collected l)ytlie Academy's Expedition to the BeriDuda 

 Islands ill 1888 under the direction of Professor Aii.<,^elo Heilprin. 

 The species obtained with the exception of the Holothurians were 

 all convnion, widely distributed forms, but of the six species of the 

 latter four were new. The limited habitat of so many members of 

 tliis group is probably due to their poor locomotory qualifications. 



It is of some interest to make a comparison of the species collected 

 in Yucatan, at Vera Cruz and in Bermuda. The Holothurians 

 found at Yucatan, three species of the genus Holotliuria, are dis- 

 tinct from the three species of the same genus collected in Ber- 

 muda. Three other species representing the genera Semperia and 

 Stichopus were also obtained in Bermuda. Of the Sea Urchins, one 

 species is common to Yucatan and Bermuda, two species are com- 

 mon to Vera Cruz and Bermuda. Melllta pentaporus at Vera 

 Cruz is represented by Melllta sexforis in Bermuda : and two species 

 were found in Bermuda which were not obtained in Yucatan or at 

 Vera Cruz. The two species of starfishes from Yucatan, and the 

 two from Vera Cruz are generically different from the two species 

 obtained at Bermuda. The two species of Ophiurans diflfer gener- 

 ically from the six species collected in Bermuda. Considerable 

 local difference in the littoral Echinoderm fauna is thus .seen to 

 exist between these three portions of the West Indian region. 



It is remarkable that the common West Indian species Toxopne- 

 ii.stes variegatus was not collected at Vera Cruz, although three other 

 species of sea urchin are abundant in that locality. It was the only 

 species of sea urchin collected in Yucatan. Can it be that at Vera 

 Cruz its place is taken by Ecliinometra suhangularis f 



It is a noteworthy fact that although Diadevia setosum is found in 

 the West Indies, upon the West African coast and throughout the 

 Indo-Pacific region, it is absent upon the west coast of America. 

 A large number of species of Holothurians, Sea Urchins, Starfishes 

 and Ophiurans, although not found in the Atlantic tropical region, 

 are similarly distributed throughout the entire Indo-Pacific region, 

 being ])resent in the islands of the Pacific, the East Indies, the In- 

 dian Ocean and upon the Eastern Coast of Africa, and resemble Dia- 

 dema setosum in their absence, with a few rare exceptions, from the 

 West Coast of America. This interesting fact appears to me expli- 

 cable in the following way : — The littoml species of the tropical 

 regions are probably distributed principally by the warm equa- 

 torial currents flowing from east to west. The equatorial currents 



