the Residence of certain Fishes. 231 



on this, namely, whether the shells now supposed, from certain 

 analogies and peculiarities of structure, to have been inhabitants 

 of fresh-water lakes, may not have equally existed in salt lakes, 

 or even in the sea. Some experiments towards the elucidation of 

 this subject have been instituted in France; but I need not detail 

 them, as they must be fresh in the recollection of all the readers 

 of this Journal. It has also been recently ascertained by M. 

 Freminville, that in the gulf of Livonia, the shell fish which 

 usually inhabit the sea, and those which belong to fresh waters, 

 are found living together in the same places. While these con- 

 firm the general presumption which forms the basis of this com- 

 munication, their general probability is also strengthened by that 

 analogy. A few facts of common occurrence on our own shores, 

 seem to add additional weight to the opinion that the testaceous 

 fishes in general are not rigidly limited to one kind of water, but 

 are capable of living in both. 



On our sea coasts, the common muscle is invariably larger and 

 fatter at the entrance of fresh-water streams into the sea, par- 

 ticularly if these bring down mud, and in these places the water is 

 scarcely salt ; yet they live also and propagate in abundance on 

 shores which receive no fresh water. The oyster is transported 

 from the sea to brackish water, where it also, not only lives, but 

 improves in condition. In the same manner the common cockle 

 inhabits indifferently the muddy sand-banks near the sestuaries 

 of rivers, which are always soaked with fresh water, and those 

 sandy or half muddy shores where no such water is found. These 

 are by no means the whole of the instances which might be enu- 

 merated in support of an opinion, of which the determination is 

 so important in the present state of geological science ; but as this 

 subject is too important to pass lightly over, and as the bounds 

 of this communication are already exceeded, I shall leave it to 

 those who may have the means and the inclination to examine it 

 in greater detail. I will only add, that the same considerations 

 will lead to similar doubts, where it has been attempted by geolo- 

 gists to determine the nature of strata, as to their marine or fresh 

 water origin, by that of the remains of fishes found in them. 



