INHABIT DIFFERENT SITUATIONS. 291 



observes that he has kept Neritina for some time alive in a 

 close vessel of salt water, which they appear to purify. The 

 animals of some of the tropical species often quit the stream 

 and crawl up the trunks of neighbouring trees, on which, 

 like the species of Littorina, Planaxis, and Bulla, which 

 creep up the rocks on the sea-coast, they attach themselves, 

 and remain exposed to the influence of the sun. It may be 

 added, that M. Rang has found Neritina auricula in brack- 

 ish marshes near the sea in the Island of Bourbon, in com- 

 pany with Aviculse and Aplysiae ; and I have little doubt 

 that Neritina pupa inhabits the sea, it being uniformly 

 brought to this country in company with marine shells. 



Many species of Melania, as, for example, M. amarula, 

 M. fasciolata, and M. lineata, are found in the freshwater 

 streams of India and its islands. Mr. Say mentions species 

 found in similar situations in North America ; he also de- 

 scribes one (M. simplex) as found in a stream running 

 through the saltwater valley near the salt-works, but does 

 not state whether the water of the stream is salt or fresh. 

 On the other hand, M. Quoy asserts that they are some- 

 times taken in brackish water ; M. Cailliaud states that 

 Melania oweni is found in brackish water ; and M. Rang 

 has found other species in the Island of Bourbon under the 

 same circumstances with the Neritina just adverted to. The 

 genus Melanopsis has the same habits ; its species are often 

 found in large inland lakes. I have myself received M. 

 buccinoidea from the sea of Galilee ; and Dr. Clark, in his 

 Travels, vol. ii. p. 24>3, figures M. dufourii under the name 

 of Buccinum galileum. The water of this lake, however, 

 unlike that of the neighbouring Dead Sea, is, according to 

 the statement of Fuller, perfectly fresh and sweet. M. 

 Lesson, on the other hand, states that he found the Pyrena 

 terebrans, regarded by M. de Ferussac as a Melanopsis, in 

 great abundance in brackish marshes in New Guinea, and at 

 the Island of Bourou. 



I am informed by Mr. Sowerby that some species of the 

 fluviatile genus Cyrena are found in the sea on the coast of 

 South America ; but he thinks it probable that the part of 

 the sea in which they are met with may be fresh, like certain 

 parts of the ocean described by Dr. Abel in his voyage to 

 China. It would be highly interesting to procure a verifica- 

 tion of this observation. Similar phenomena may not be 

 uncommon, for I have myself observed in Torbay a small 

 space in the neighbourhood of Brixham, the water of which 

 was of a different colour and much fresher than that of other 

 parts of the bay. With reference to another species of the 



u 2 



