MOLLUSCS 321 



to the British Museum proved to be of some value and 

 interest.! 



Woodlice, like other creatures such as earwigs, scor- 

 pions and centipedes, usually regarded as objectionable, 

 were exceptionally scarce on the islands, and this was 

 very surprising, for one would have expected a com- 

 paratively equable, damp climate to afford favourable 

 conditions. 



Molluscs. 



The lake shore abounded with univalves and bivalves 

 which had quite a marine appearance ; securely fastened 

 to rocks was a species resembling the common oyster. 

 Besides these were others very closely resembling our 

 English genera of fresh-water snails and mussels. 



A curious slug, that had very short tentacles 

 and seemed to have no " mantle " at all, was found 

 slowly crawling on wet sand, where also the large Ampul- 

 laria were occasionally thrown up by waves. Shells of 

 these large molluscs may be found on the lake shore, 

 apparently battered to pieces on a stone as our garden 

 snails are by thrushes. I strongly suspect this to be 

 the work of the " open-bill " stork. 



On Damba Island there was found quite commonly a 

 snail of the type of our English Vitrina, but very much 

 larger, with a thin fragile shell practically enveloped by 

 extensions from the mantle. This was easily procured in 

 numbers when the " Ensanafu " ant had been hunting, for 

 its only means of escape was to crawl upwards. Should 

 it happen to come to the top of a stem it was unable to 

 descend again and face the ants, so defended itself by emit- 

 ting bubbles to form a mass of foani completely surround- 

 ing itself, which the ants could not penetrate, and if they 

 bit into it they could reach nothing solid. These white 

 masses of foam, like " Cuckoo spit," were very con- 



^ Dolops ranarum and Argulus ajricanus. 

 22 



