EBUllNA. 95 



because the building organ reaches only to the lip^ from 

 which the shell gradually recedes in its progress of growth. 

 One and the same purpose is_, therefore, effected by 

 different means, which are equally beautiful and curious 

 in their results. But, though the shell of the Olive offers 

 no outward indication of progressive growth, yet, if the 

 outer coat be removed by chemical agency, a superincum- 

 bent layer of different colour and design becomes visible. 

 Thus, while the external coating of the Oliva utnculus is 

 of an obscure milky blue tinge, a dark ashy ground, 

 sprinkled with numerous triangular opal-like dashes, is 

 revealed by the application of an acid; thus, also, when 

 the outer layer of the Oliua Brasiliensis is removed,, a 

 longitudinally striped pattern becomes apparent. 



Olives are confined exclusively to the tropical regions. 



The genus Ebiirna includes a natural, though extremely 

 limited, group of species ; and, although a peculiarity of 

 colour is rarely regarded as an element in the character of 

 a genus, it constitutes, in the present instance, a feature 

 which cannot be overlooked. The species are each distin- 

 guished by a blotched and tessellated painting of orange- 

 brown, upon a white ground ; the apex throughout is black, 

 and the columella and interior of the aperture white. 



