Verrill, Notes on Radiata. 35 1 



exchange in the other direction. Such is found to be the case ; no 

 species fairly belonging to the exclusive Pacific fauna being found in 

 the West Indies." 



The higher level of the Atlantic Ocean is, however, denied by- 

 others, and in consequence of the slight tides of the Atlantic side and 

 their great rise and fall on the Pacific side, it is quite as probable that 

 in case of a communication by means of a shallow or narrow channel, 

 currents would fiow alternately in each direction. 



It is nevertheless very apparent that an intercommunication more 

 or less remote between the two oceans cannot of itself account for 

 the relations between the two faunae, for should we assume that the 

 small per-cent of identical species can be accounted for in this way, 

 the occurrence of very large numbers of closely allied but distinct 

 species, and also the agreement in generic and family types, already 

 pointed out, still remain to be explained. This part of the subject 

 presents much greater difiiculties than the identity of a few species. 



Two entii-ely distinct theories have been, and will doubtless long 

 continue to be, adopted by naturalists in explanation of these facts 

 and similar ones in various other regions : 



1st. That the species and genera were created as we find them, and 

 were originally adapted to the physical conditions and peculiarities 

 of their respective districts. Consequently we should expect to find 

 similar regions inhabited, to a greater or less extent, by similar genera 

 and species. 



2nd. That an extensive intercommunication took place at a remote 

 period, and that the similar and allied species found upon the opposite 

 coasts have originated by gradual differentiation from common ances- 

 tors, after the separation of the two oceans. 



No. 4. — Notice of the Corals aiid Echinoderms collected hy Prof. C. F. 

 Hartt, at the Ahrolhos Reefs^ Province of Bahia^ Brazil^ 1867. 



Published, February, 1868. 



The collections of Radiata made by Mr. Hartt during the summer 

 of 1867, while examining the coral-reefs which he had previously 

 discovered upon the coast of Brazil,* having been submitted to me for 

 examination, were found to contain so many species yet undescribed 



* Mr. Hartt was a member of the party that accompanied Prof. Agassiz, in his cele- 

 brated Expedition to Brazil and,* while making a special exploration of the coast, at that 

 time first discovered some of the reefs n6ar Santa Cruz and Porto Seguro. 



Trans. Connecticut Acad., Vol. I. 45 February, 1868. 



