16 ENGLAND TO RIO DE JANEIRO CHAP, i 



these stung the person who touched them in the same 

 manner as nettles, only much more severely. On the top 

 of this bladder was a membrane which he turned either one 

 way or the other to receive the wind ; this was veined with 

 pink, in an uncommonly beautiful manner; in short, the 

 whole was one of the most beautiful sights I have seen 

 among the mollusca, though many of them are beautiful. 



The floating shells, Helix ianthina 1 and violacea, from 

 their particularity, also deserve mention. They are to be 

 found floating on the top of the water by means of a small 

 cluster of bubbles filled with air, composed of a tenacious 

 slimy substance, not easily parting with its contents ; these 

 keep them suspended on the surface of the water, and serve 

 as a nidus for their eggs : it is probable that they never go 

 down to the bottom, or willingly come near any shore, as 

 the shell is of so brittle a, construction that few sea-water 

 snails are so thin. 



Every shell contains within it about a teaspoonful of 

 liquid, which it freely discharges on being touched ; this is 

 of a most beautiful red purple colour, and easily dyes linen 

 clothes ; it may be well worth inquiry whether or not this 

 is the purpura 2 of the ancients, as the shell is certainly found 

 in the Mediterranean. We have not yet taken a sufficient 

 quantity of the shells to try the experiment, perhaps we 

 shall soon. 



Procellaria oceanica differs very little from P. pelagica, 

 Linn., but from his place of abode so far south, and some 

 small difference in plumage, it is more than likely that he 

 is different in species. 



9th. Found two new species of Lepas (vittata and midas) 

 on the stern of the ship ; they were both sticking to the 

 bottom, in company with L. anatifera, of which there was 

 great abundance. 



IQth. Took plenty of Helix ianthina and some few of 

 violacea. Shot the black-toed gull of Pennant ; it had not 



1 These two species are not Helices, but belong to the genus Ianthina. 



2 The purple of the ancients has since been proved to have been derived 

 from a species of Murex or of Purpura. 



