CO^CHYUX—DITHYRA. 48. 219 



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

 and have no lesser ones between them. 



48. AMCVLA— LAMARCK. 



Testa depressa, obliqua, inaquivahis, inoiquilateralis ; basi 

 transversim rcctiltneari, titrinque lohatd ; umbonilms renw- 

 tiusculis. Cardo linearis, dente tinico subpenetrante : late- 

 ralibns nuUis. Ligamentum liiieare, externum. 



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

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

 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 

 lengthened 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 «. Hence it has been denominated the swallow-itail' 

 Mussel. 



2f 2 



