426 MANUAL OF THE MOLLUSCA. 



with a semicircular row of transverse teeth; adductors sub- 

 equal ; pallial line simple ; margins crenated inside. 



Animal with a large crescent-shaped foot, margins of the 

 sole undulated ; mantle open, margins simple, with minute 

 ocelli ; gills equal, lips continuous with the gills. 



Distribution, 58 species. West Indies, Britain, India, New 

 Zealand, "West America; ranging from 8 to 60, rarely 120 

 fathoms. 



Fossil, 80 species. Neocomian — . United States, Europe 

 South India. 



The teeth of Pedunculus and Area increase in number with 

 age, by additions to each end of the hinge-line, but sometimes 

 the central teeth are obliterated by encroachments of the liga- 

 ment. 



LiMOPSis, Sassi, 1827. 



Type, L. aurita, PI. XYII., Fig. 17. 



Synonym, Trigonoccelia, Nyst. Pectunculina, D'Orb. 



Shell orbicular, convex, slightly oblique ; ligamental area 

 with a triangular cartilage-pit in the centre ; hinge with 2 

 equal, curved series of transverse teeth. 



Distrihution, 4 species. Eed Sea (Nyst.), Japan, Britain. 

 Mr. M 'Andrew has dredged L. pygmcea, living, on the coast 

 of Finmark ; it is a fossil of the Pliocene of England, Belgium, 

 and Sicily. 



Fossil, 36 species. Bath-oolite — . United States Europe. 



NucuLA, Lam. 



Etymology, diminutive of mix, a nut. 



Example, N. Cobboldise, PL XVII., Fig. 18 



Shell trigonal, with the umbones turned towards the short 

 jposterior 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 ; paUial 

 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 con- 

 voluted appendage ; gills small, plume-like, united behind the 

 foot to the branchial septum. 



The Nucula uses its foot for burrowing, and Professor 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 



