288 



certainly the most valuable of this genus, though many 

 other species are of greater rarity. 



Lamarck observes that many species exist, but 

 their determination is difficult, as the characters (inde- 

 pendent of the markings and colors of the shell), are 

 not numerous or much varied. It is however very desir- 

 able that some more natural chain of approximation 

 should be established between them ; many species pos- 

 sessing sufficiently marked characters to guide the Na- 

 turalist in that task. 



Cypraea cervina 



Cypraea tigris 



exanthema 



tigrina 



Argus 



talpa 



• testudinaria 



carneola 



Mauritiana 



lurida 



mappa 



vitellus 



Arabica 



caput-serpentis 



histrio 



....... cinerea 



scurra 



zbnata 



rattus 



sordida 



stercoraria 



icterina 



mus 



miliaris 



ventriculus 



variolaria 



aurora 



rufa 



