Mr Gray on Testaceous Molhiscn. ' 89 



to. The genus Melanopsis has the same habits ; its species are 

 often found in large inland lakes. I have myself received J/. 

 htccinoidea from the sea of Galilee ; and Dr Clark, in his Tra- 

 vels, vol. ii. p. 243, figures M. Ditfourii under the name of 

 Buccinum Galileum. The water of this lake, however, unlike 

 that of the neighbouring Dead Sea, is, according to the state- 

 ment 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 brack* 

 ish marshes in New Guinea, and at the Island of Bourou. 



I am informed by Mr Sowerby that some species of the flu- 

 viatile 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 verification of this observation. 

 Similar phenomena may not be uncommon, for I have myself 

 observed in Torbay a small space in the neighbourhood of Brix- 

 ham, 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 same genus, Cyrena Vanikorejisis^ M. 

 Quoy observes : — " Ne I'ayant pas trouvee dans les lieux mare- 

 cageux mais sur les bords de la mer, il est probable qu'elle vit a 

 rembouchure des rivieres qui sont saumatres a maree haute.*"* 



The third class of cases, in which species of Mollusca that are 

 generally found in the sea are taken in fresh water, is much 

 more rare than the preceding. It is obvious that in such in- 

 stances the animal must be possessed of the capability of adapt- 

 inff itself to the different characters of the two fluids. This ca- 

 pability exists in much more highly organized animals, such as 

 fishes, many species of which constantly migrate from the sea 

 and ascend the rivers to deposit their spawn ; but in these cases 

 it is the result of a regular and determinate habit, while in the 

 Mollusca it appears to be entirely dependent on accidental cir- 

 cumstances. 



In some marshes in the Island of Bourbon, in which the water 

 is almost fresh, M. Rang has observed specimens of Aplysia 

 dolahrifera in company with Neritince and Melanioe. 

 • Voyage de 1' Astrolabe, torn. iiL p. 516. 



