CONCHIFERA. 269 



NUCULA, Lam. 



Etym. Diminutive of nux, a nut. Ex. N. Cobboldise, PI. XVII. fig. 18. 



Shell trigonal, with the umbones turned towards the short posterior side ; 

 smooth or sculptured, epidermis olive, interior pearly, margins crenulated ; 

 hinge with prominent internal cartilage -pit, and a series of sharp teeth on 

 each side ; pallial line simple. 



Animal with the mantle open, its margins plain; foot large, deeply 

 fissured in front, forming when expanded a disk with serrated margins; 

 mouth and lips minute, palpi very large, rounded, strongly plaited inside and 

 furnished with a long convoluted appendage ; gills small, plume-like, united 

 behind the foot to the branchial septum. 



The Nucula uses its foot for burrowing, and Prof. Forbes has seen it 

 creep up the side of a glass of sea-water. The labial appendages protrude 

 from the shell at the same time with the foot. N. mirabilis, Adams, from 

 Japan, is sculptured like the extinct N. Cobboldite. 



Distr. 70 sp. U. S. Norway, Cape, Japan, Sitka, Chile. On coarse 

 bottoms, from 5100 fms. 



Fossil, 100 sp. L. Silurian ? . Trias . America, Europe, India. 



Sub-genera. Nuculina, D'Orb.* 1847. N. miliaris, PI. XVII. fig. 19. 

 Shell minute ; teeth few, in one series, with a posterior lateral tooth. Eocene, 

 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. 



? Stalaymium (margaritaceum) Conrad, 1833 = Myoparo costatus, Lea, 

 Eocene, Alabama. ? S. Nystii, Galeotti (Nucunella, D'Orb. Eocene, Bel- 

 gium. Shell like Limopsis ; ligamental area narrow, wholly posterior. 

 ISOARCA, Miinster, 1842. 



Type, I. subspirata, M. Oxford Clay ; France, Germany. 



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 (Ctenodonta) Salter, L. Silurian, Canada, is 3 inches-long and 

 has the ligament preserved. 



Fossil, 14 sp. L. Silurian Chalk. N. America ; Europe. 



Sub-genus. Cucullella, M'Coy. C. antiqua, Sby. U. Silurian, Hereford- 

 shire. Shell elliptical, with a strong rib behind the anterior adductor 

 impression. 



LEDA, Schumacher. 



Etym. Leda, in Greek myth, mother of Castor and Pollux. 



Syn. Lembulus (Leach) Bisso. Ex. L. caudata, PI. XVII. fig. 20. 



Shell resembling Nucula ; oblong, rounded in front, produced and pointed 



* N. donaciformis, Parreyss, from the White Nile, is a crustacean ! (Eatheria). 



