172 LIGULA. 



lateral tooth each side, the segments of which divaricate from the 

 beak." To represent this genus we have figured L. Squamosum 

 in the plates, fig. 62. British. 



LEPTOSPIRA. Sw. A sub-genus of Bulinus, thus described : 

 (i Spire excessively long, sub-cylindrical ; body whorl largest ; 

 outer lip thickened; aperture oval ; no teeth, striata, Sw. Chem. 

 135. f. 1226. signata Sw.' y Sw. p. 335. 



LEUCOSTOMA. Sw. A genus of " Achatina," Sw. described as 

 resembling Achatinella, but having a " thick pad" at the top of 

 the iS upper lip," and another over the base. L. variegata, Sw. 

 Lardn. Cyclop. Malac. fig. 24. p. 172. 



LEUCOTUS. Sw. A sub-genus of Natica, described as interme- 

 diate between Sigaretus and Lacuna. Sigaretus cancellatus, 

 Lam. (Sw. Malac. p. 346.) 



LICTUM. Humph. Ovula, Lam. (Ovulum.) 



LIGAMENT. (From Ligo, to bind.) The true ligament is always 

 external, and serves the purpose of binding the two valves of a 

 shell together externally by the posterior dorsal margins. There 

 is another substance, called by Gray the Cartilage, which is 

 elastic and of a condensed fibrous structure, placed within the 

 ligament, either close to it, or at a more interior part of the shell ; 

 it is sometimes contained in a pit, formed for its reception, in 

 the centre of the hinge. This substance, being elastic, keeps the 

 valves open, unless drawn together by the counteracting force of 

 the adductor muscles. When conchologists speak of a shell as 

 having the ligament external, the real meaning is that these two 

 substances are so close together as in appearance to constitute one 

 body placed outside the shell so as to be seen when the valves are 

 closed. When two ligaments are spoken of, as in Amphidesma, 

 the meaning is that the cartilage occupies a separate place on the 

 hinge. 



LIGAMENT1FEROUS. (Ligamentum, a ligament, fero, to bear.) 

 Having or containing the ligament, as the cardinal pit in Mya, 

 fig. 71. 



LIGULA. Leach. A genus containing the more rounded and less 

 gaping species of Lutraria, Auct. Fig. 77, Lutraria Papyracea. 



