226 ARCADiE. 



LEDA. Schumacher. 



Shell equivalve, inequilateral, oblong, produced posterior- 

 ly, closed, smooth or concentrically striated, invested by 

 an epidermis ; margins smooth ; beaks approximated, in- 

 curved ; inside more or less nacreous ; hinge-line angulated 

 and formed, as well as the ligament, as in Nucula. Pallial 

 impression with a sinus. 



Animal oblong ; mantle open in front, with simple or 

 fimbriated margins, furnished posteriorly with two partially 

 united slender unequal siphonal tubes. Foot and palps 

 like those of Nucula. 



The propriety of separating this group of bivalves from 

 Nucula was first shewn by the lamented author of the 

 " Index Molluscorum Groenlandise, 1 ' who, after having 

 discovered the peculiarities of the animals, adopted the 

 genus as empirically proposed by Schumacher. It is 

 singular that the sinuated pallial impression, indicative of 

 the presence of siphonal tubes, had previously escaped 

 notice. Leda is one of several instances which go to shew 

 the fallacy of separating the lamellibranchiate bivalves into 

 great sections on account of the presence or absence of 

 siphons. The genus ranges far back in time, and its species 

 exhibit similar habits with those of Nucula. 



L. caudata, Donovan. 



Surface girt with raised concentric striae. 

 Plate XLVII. fig. 11, 12, 13, and (Animal) plate P. fig. 2. 



Area mirntta, 0. Fabricius, Fauna Groenlandica, p. 414 ? — Mont. Test. Brit, 

 p. 140. — Maton and Rack. Linn. Trans, vol. viii. p. 92. — Dor- 

 set Catalog, p. 3G, pi. 1, f. 1G. — Turt. Conch. Diction, p. 11, 

 f. 98. — Dillw. Recent Shells, vol. i. p. 245. — Index Testa- 

 ceolog. pi. 10, Area, f. 44. 



