252 On the Question — Is there Identity betrvecn the 



The Murex angulifer is only the Murex ramosus with simple 

 prominences ; and the Murex erinaceus, subcarinatus, angu- 

 liferus^ tarentinus and polypierus. are varieties of the same 

 species. In like manner, the Murex magellanicus of tranquil 

 waters appears covered with large sharp foliaceous expan- 

 sions, while, in agitated seas, the same shell has no such ex- 

 pansions, and has only the ribs crossed. This species rarely 

 attains a large size ; when it does become large, it is solid, 

 and loses almost all the appearance of striae. 



The moditiations which shells undergo in consequence of 

 the diversity of their stations, are so much the more import- 

 ant to be noticed, since these calcareous pieces are almost 

 the only remains of the mollusca of the ancient world that 

 have come down to us. Similar effects are not less sensible 

 on fresh water molluscs. Lymnwus pereger furnishes us with 

 a remarkable example of such changes. When the rivers 

 of Sweden, and probably of other places, carry it to the Bal- 

 tic, it is so modified by the different nature of the waters in 

 which it is successively plunged, that it cannot be recognised. 

 To such a degree is this carried, that it has been regarded as 

 another species, and another specific name assigned to it. 



Similar modifications have likewise taken place in other 

 species of the same genus, in Lymnceus ovatiis for example, 

 and that from causes less powerful and less active than those 

 whose effects are so obvious on Lymnceus pereger. It would 

 undoubtedly happen that, if we could not observe in what 

 manner these modifications are brought about, if we could 

 not follow their gradations, and observe the transitions of 

 these shells into one another, we would create them into 

 arbitrary species, since they would not be founded on the na- 

 ture of things. 



We may remark, in relation to shells, that there are mul- 

 titudes of them whose characters we appreciate only by the 

 assistance of the monies, whether interior or exterior, from 

 which we may judge of the degree of uncertainty we must be 

 in when we proceed on this single means of determination. 

 In fact, these monies undergo numerous variations, according 

 to their degree of preservation ; it may even happen, from a 

 series of accidental circumstances, that they present charac- 



