Manchester Memoirs, Vo/. x/v. (igoi), No. 14. 19 



None of the species has been taken in the tropics in 

 deep or shallow water. 



I have mentioned four cases in which southern species 

 are very nearly related to northern species. 



In only two cases ( Arenicola assimilis (?) and A. 

 claparedii) have we any evidence whatever of an inter- 

 passage of forms along the western shores of America, 

 and, as these forms have not been taken at intermediate 

 stations along the Pacific coast between California and the 

 Straits of Magellan, the generality of such transference is 

 by no means proved. 



On the other hand, both these species occur on 

 European shores, and, as I have previously stated, their 

 free-swimming larval stage is limited to so short a period 

 that it is impossible that they could cross the Atlantic. 

 Moreover, as 41° N. appears to be the northern limit of 

 the genus, it is impossible that these forms could find 

 their way into the Atlantic along the northern shores of 

 North America. 



In no case have we any evidence of an interchange 

 of species along the western shores of Africa, and I have 

 shown that, in the genus Goniada, the same species may 

 be present in the temperate north and south Atlantic, but 

 along the tropical western shores of Africa the genus is 

 represented by several distinct and modified species. 



These results, to my mind, increase the evidence in 

 favour of the Pfeffer and Murray " Bipolar Theory " for 

 the littoral fauna. 



The work in connection with these papers has been 

 done in the zoological laboratories of the Owens College 

 with the help of a grant from the Government Grant 

 Committee of the Royal Society. My research has been 

 supervised by Professor Hickson, to whom I am greatly 

 indebted for much valuable assistance and advice. My 



