262 Contribution to our knowledge of Pelagic Mollusca. [No. 4, 



The table (see p. 269,) accompanying this, has reference merely to 

 those Pteropods which are furnished with an external shell ; the 

 Thecosomata of de Blainville. It shows that the — 



Atlantic Ocean contributed 23 species. 



Indian Ocean „ 23 ,, 



Southern Ocean ,, 11 ,, 



Bay of Bengal „ 11 ,, 



It will also be seen that the majority of those species can bear a 

 great difference of temperature, for example H. uncinate, CI. ryyrami- 

 data, Spirialis rostrcdis. On such as these the currents have doubt- 

 less a strong diffusive influence, and although the Cape of Good Hope 

 may serve in some measure to isolate the fauna of the Indian Ocean, 

 yet the number of species in the South Atlantic common to it, 

 proves that the two populations do mingle,* and not only so, but that 

 some of the fauna of the Indian Ocean finds its way up to, and doubt- 

 less through the great equatorial current in the Atlantic. f 



As far as my own observations go, and from what I have gathered 

 from those of others in the same field, I think the following species 

 are peculiar to that portion of the North Atlantic through which out- 

 ward ships shape their course — 



1. Ilyalcea tcniourancJu'a, 



2. //. longirostra, 



3. H. mucronata (?) 



4. Chodora balantium, 



also the large coloured variety of H. gihbosa, figured by Rang, pi. x, 

 figs. 3 and 4. 



To the Indian Ocean, or more properly speaking, the Indo-Pacijic 

 province| I would assign the following species — 



1. Hyalcea fiava, 



2. H. glohulosa, 



3. H. affinis, 



4. S. tridentata (?) 



* The drift current of the S. E. trade wind doubtless having much to do 

 with this. 



f Woodward. 



X A bottle thrown overboard 2\ leagues N. E. of Ascension from the Ame- 

 rican ship Lady Montagu in October 1820, was picked up on the Hunway rocks 

 on the West coast of Guernsey in August, 1821. 



Vide p. 155 of the Naut. Mag. for 1854. 



