CONCHIFERA. 427 



foot. N. mirahiUs, Adams, from Japan, is sculptured like the 

 extinct N. CohhoMice. 



Distribution, 70 species. United States, Norway, Cape, 

 Japan, Sitka, Chili. On coarse bottoms, from 5 — 100 fatlioms. 



i^oss?7, 177 species. Lower Silurian ? — . Trias — . America, 

 Europe, India. 



Sub-genera. Nucidina, D'Orh* 1847. N. miliaris, PI. XYII., 

 Fig. 19. Shell minute ; teeth few, in one series, with a posterior 

 lateral tooth. Eocene, France. Nucinella (ovalis), Searles- 

 AVood, 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. Eocene, Alabama. ? S.N'ystii, Galeotti (Xucunella, 

 D'Orb.). Eocene, Belgium. Shell like Limopsis ; ligamental 

 area narrow, wholly posterior. 



IsoARCA, Miinster, 1842. 



Type, I. 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. 



/. Loyani (Ctenodonta), Salter, Lower Silurian, Canada, is 

 3 inches long, and has the ligament preserved. 



Fossil, 14 species. Lower Siluiian — Chalk. North America. 

 Europe. 



Suh-yenera. Cucullella, M'Coy. C. antiqua, Sby. Upper 

 Silurian, Herefordshire. Shell elliptical, with a strong rib 

 behind the anterior adductor impression. 



Lunidarca, Gray. Part anterior to the umbo toothless, with 

 a lunule. 



Leda, Schumacher. 



Etymology, Leda, in Greek mythology, mother of Castor and 

 PoUux. 



Synonym, Lembulus (Leach) Eisso. 



Example, L. caudata, PL XVII., Fig. 20. 



Shell resembling Nur.ida ; oblong, rounded in front, p -ohiced 

 and pointed behind; margins even; pallial line with a snail 

 sinus ; umbonal area with a linear impression joining the a-ite- 

 rior adductor. 



Animal furnished with two partially-united, slender, unequ il, 



* N. donaciformis, Parreyss, from the White Nile, is a crustacean ! ;Estheria.) 



