CONCHIFERA : 427 
foot. N. mirabilis, Adams, from Japan, is sculptured like the 
extinct N. Cobboldic. 
Distribution, 70 species. United States, Norway, Cape, 
Japan, Sitka, Chili. On coarse bottoms, from 5—100 fathoms. 
Fossil, 177 species. Lower Silurian?—. Trias—. America, 
Hurope, India. 
Sub-genera. Nuculina, D’Orb.* 1847. N. miliaris, Pl. XVILI., 
Fig. 19. Shell minute; teeth few, in one series, with a posterior 
lateral tooth. Hocene, France. Nucinella (ovalis), Searles- 
Wood, 1850 (+ Pleurodon, Wood, 1840), a minute shell from 
the Coralline crag of Suffolk, is described as having an external 
ligament. 
? Stalagmium (margaritaceum), Conrad, 1833—Myoparo cos- 
tatus, Lea. Hocene, Alabama. ? S.Nystii, Galeotti (Nucunella, 
D’Orb.). Hocene, Belgium. Shell like Limopsis; ligamental 
area narrow, wholly posterior. 
Isoarca, Minster, 1842. 
Type, 1. subspirata, M. Oxford Clay, France, Germany. 
Synonym, Noetia, Gray. 
Shell ventricose; beaks large, anterior, often sub-spiral; 
ligament entirely external; hinge-line curved, with two series 
of transverse teeth, smallest in the centre; pallial line simple. 
I. Logani (Ctevodonta), Salter, Lower Silurian, Canada, is 
3 inches long, and has the ligament preserved. 
Fossii, 14 species. Lower Silurian—Chalk. North America. 
Europe. 
Sub-genera, Cucullella, M‘Coy. C. antiqua, Sby. Upper 
Silurian, Herefordshire. Shell elliptical, with a strong rib 
behind the anterior adductor impression. 
Lunularca, Gray. Part anterior to the umbo toothless, with 
a lunule. 
LEDA, Schumacher. 
Etymology, Leda, in Greek mythology, mother of Castor and 
Pollux. 
Synonym, Lembulus (Leach) Risso. 
Haxample, L. caudata, Pl. XVII., Fig. 20. 
Shell resembling Nucula; oblong, rounded in front, produced 
and pointed behind; margins eyen; pallial line with a small 
sinus; umbonal area with a linear impression joining the ante- 
rior adductor. 
Animal furnished with two partially-united, slender, unequ il, 
* N. donaciformis, Parreyss, from the White Nile, is a crustacean! (Estheria.) 
