CO'^CRYLIA—DITHYRA. 48. 219 



longitudinal lines are more remote, in a nearly straight direction, 

 and have no lesser ones between them. 



48. AY1C\jLA— LAMARCK. 



Testa depressa, ohliqua, ineBquiialvis, inaquilateralis j basi transversim 

 rectilineari, utrinqu^ lohatd ; umbonibus remotiusculis. Car do 

 linearis, dente unico subpenetrante : lateralibus nullis. Ligamentum 

 lineare, externum. 



Shell flat, oblique, inequivalve, inequilateral ; transversely pro- 

 duced in a straight line at the base, where the sides are lobed j 

 the beaks rather remote. Hinge linear, with a single slightly 

 penetrating tooth : lateral teeth none. Ligament linear, ex- 

 ternal. 



The general outline of this genus is rather singular. From a 

 straight and elongated base rises obliquely the rounded or oval body 

 of the shell : and when the valves are expanded, with the length- 

 ened processes downwards, it has some sort of resemblance to a bird 

 on the wing ; the valves representing the wings, as at letter b of our 

 figure, and the elongated processes the tail, as at the letter a. 

 Hence it has been denominated the swallow-tail Mussel. 



2f 2 



