94 



CHAPTER XVI. 



THE 'swallow' mussel. — AVICULA. — PINNA AND ITS BEARD. — THE 

 FABLE, SHARP-TOOTHED NUCULA. — LEDA. ARCA. PECTUNCULUS. 



AVICULIDJE AND ARCADE. 



In the first of these families we boast one Avicula and one 

 Pinna. 



Avicula Tarentina is also known as Mytilus hinmdo, 

 from a fancied resemblance in the graceful form of its shell 

 to that of a swallow in flight. Mr. Hanlej compares it to 

 a mussel placed obliquely, with a long wing-shaped appen- 

 dage attached horizontally to its apex. The hinge and me- 

 dial disc within is beautifully iridescent, as might be ex- 

 pected from its afhnity to the pearl-oyster of the orientals ; 

 the outside of the shell is of a loose scaly texture, almost as 

 much so as that of the oyster ; the foot, or locomotive organ, 

 of the Avicula being small, the byssus,or means of anchorage, 

 is proportionately large. 



