348 ERNEST WARIJKN. 



Oat of the 32 Natal species 13 occur in xVustralia or New 

 Zealand, 6 in the Cape, 6 in Europe, and 6 in America. 



It is noteworthy that more Cape species have not been 

 found in Natal. As far as I am aware no hydroid faunistic 

 lists from the Cape coast have been published, but a consider- 

 able number of species have been described, and yet out of 

 the 32 Natal hydroids collected only 6 Cape species have been 

 found. 



There is an obvious affinity between the Natal and Australian 

 hydroid fauna?, and the list points to the view that this 

 affinity may be stronger than that between the Natal and the 

 Cape faunte. 



This apparent difference in the hydroid fauna} is perhaps 

 associated with the course of the ocean currents. The warm 

 south equatorial cui-rent flows westwards, and a part of it is 

 deflected southwards as the Natal or Mozambicpie Current. 

 This Hows along- the east coast of the Cape until it meets the 

 cold Antarctic Current at the Agulhas Bank, when the greater 

 part of it turns eastwards and flows back to Australia and 

 then passes northwards up the west coast of the continent to 

 be again caught up in the south Equatoi-ial Current. 



It is hence readily understood why there should be a marked 

 diiference between the mai'ine fauna of the Natal coast and 

 that of the Cape coast, especially the part west of the Angulhas 

 Bank, since here the influence of the cold Antarctic Current 

 is more strongly felt. 



III. 



Note on the Nematocysts. 



After the measurements of the nematocysts in the various 

 species were made, it was felt that there was some relationship 

 in the shape of the nematocyst and the family to which the 

 species belonged ; in other words, that species of the same 

 family tended to have nematocysts of similar shape. 



In the accompanying table the second column gives the 

 approximate length of the hydranth ; the third, fifth, and 

 seventh columns give respectively the length (j>) and In-eadth 



