200 INTRODUCTION' TO CONCHOLOGY. 



and smooth shelly the upper surface rather convex and 

 generally white, the vertex being small and situated near 

 the centre ; the under surface is slightly concave, the 

 central disc of a brown yellowish rich colour, with an 

 irregular, continuous, muscular impression running round it. 

 Little is known with certainty concerning these sin- 

 gular mollusks. One thing, however, is certain — they 

 cannot give utterance to any emotions that may dwell 

 within them. A modern writer has beautifully remarked, 

 that harmony is nature''s homage ; it may be found in the 

 rolling wave, that foams upon the rugged coast, as well as 

 in the silent murmuring of the rippling stream. In ani- 

 mated nature, the melody of sweet sounds is more palpable 

 to the ear, for in our gardens and about our dwellings the 

 birds never cease to please us with an endless variety of 

 song ; but from whatever source such harmony arises, 

 whether from things animate or inanimate, certain it is, 

 that mollusks are silent. This is a curious fact, of which 

 the insect tribes present but few examples. Insects, in- 

 deed, are voiceless, in the usual acceptation of the word, 

 but they possess the language of signs, and these they are 

 singularly enabled to render audible. 



