LEDA. 153 



Genus II. LE'DA*, Schumacher. PL IV. f. 2. 



BODY transversely oval : mantle open in front, as well as on 

 the anterior side, and forming on the posterior side two cylin- 

 drical tubes of unequal length. Other characters as in Nucula. 



SHELL triangular- oval, or oblong : margin produced on the 

 posterior side, and in some species slightly gaping or open : 

 lunule lance-shaped : ligament, cartilage, and teeth as in Nucula, 

 except that the number of teeth on the anterior side is nearly 

 equal to that on the posterior side : pallial scar interrupted by 

 the tubes. 



This genus is closely allied to Nucula in its distribu- 

 tion and habits, as well as in most of the characters exhi- 

 bited by the animal and shell ; but the mantle in Leda 

 forms two distinct tubes, and the shape of the shell is 

 oval or oblong, instead of triangular as in Nucula. The 

 teeth, also, in the present genus are set more obliquely, 

 and the disparity of number is less between those in the 

 front and those in the back row. It corresponds with 

 the genus Lembulus of Leach, quoted by Eisso; and 

 according to Morch (' Gron'lands Bloddyr ') it is Link's 

 genus Nuculana, a name of prior date to that of 

 Schumacher. 



Holler's genus Yoldia is said to differ from Leda in 

 the tubes being longer, and curved instead of straight, in 

 the foot being larger and thicker, in the posterior edges 

 of the mantle being ciliated instead of plain, and in the 

 shell gaping at both ends, whereas that of Leda is closed 

 at the anterior end and truncate at the other ; and the 

 posterior side has two or three "blunt external ridges, 

 and an internal rib or epiphysis caused by the separation 

 of the tubes. But in L. minuta the posterior edges of 

 the mantle are ciliated, or fringed by short filaments, 

 and the shell of L.pygm&a, which is referred by northern 



* A proper name in Greek mythology. 



H 5 



