Holes on Lingual Dentition of Mollusca. 293 



Sc, Phila., 1863) than io Melantho diX\(\. Lioplax. (See Land and 

 Fresh-water Shells of North America, Part III., pp. 16, 35, 55, 

 etc.) 



Lingual membrane long, with the arrangement of teeth usual 

 to the family. Teeth 3.L3. The centrals are subcircalar, with 

 a truncated, irregularly horizontal base; the apex recurved, 

 channelled, and obtusely knobbed or denticulated. The first lateral 

 is about as wide as the central, oblong, bulging at the sides, trun- 

 cated and horizontal at base, its apex deeply digitated or fringed, 

 some of the denticles being recurved at their apices. The second 



Fig. 11. 



Lingual dentition of Tulotoma magniflca, Conrad. 



lateral is laminar, narrowing slightly towards the truncated base, 

 curving outward from the central tooth, its apex with long 

 fringe-like denticles, some of which are recurved, others obtusely 

 knobby. The third lateral i-esembles in shape and size the 

 second, but is somewhat less curved, and has shorter, less delicate 

 denticles. 



There is considerable variation in the number, length, delicacy 

 and arrangement of the denticles on the different teeth. In some 

 cases they are very broad, with simple recurved edges. Li others 

 they are long, narrow, and bifurcate. Again on many teeth the 

 denticles are not absolutely separated one from the other, but the 

 end of the tooth is rather deeply channelled. 



The variations occur in the laterals, the centrals being more 

 uniform. The side edge of the laterals is sometimes retiurved for 

 a considerable length. 



