398 SHELLS AND SHELL-FISH. 



Ligament. An exteranl substance, by which the two 

 valves of acephalous Testacea are united, and which, 

 in fact, is the true hinge. The internal part is gene- 

 rally composed of another substance, called the car- 

 tilage, of a compact fibrous structure, which is elastic 

 when moistened, but very hard and solid when dry. 

 This is generally placed close to the bosses, and is 

 often continued between the teeth, so as to form a 

 second or internal ligament. 



Lips. The two sides of the aperture of spiral shells are 

 termed the lips. That which joins, and generally 

 folds over, the lower part of the columella, is called 

 the inner lip, while that part of the circumference 

 opposite is the outer. The latter, of course, is found 

 in all shells, because it is the termination of the last 

 whorl ; but the inner lip is frequently absent, or only 

 indicated by a thin, whitish, almost transparent 

 enamel": sometimes, however, it is highly developed, 

 as in Nassa, the typical Cassides, or helmet-shells, 

 and several others. 



Lobed. A broad obtuse division, as in many of the 

 Strombi and Pleurotomince. 



Longitudinal. The meaning of this term, as used and 

 understood by all the best conchologists, is " length- 

 wise ;" hence it means any stripes which run in a 

 perpendicular direction from the apex to the base of 

 spiral shells, while such as are in a contrary direc- 

 tion that is, parallel to the suture of the whorls, 

 are transverse. Great confusion, therefore, is likely 

 to be introduced by reversing these definitions.* 

 However objectionable they may be thought by fas- 

 tidious persons, we always have and shall continue 

 to designate the direction of stripes, bands, or other 

 peculiarities, as longitudinal when they run in the 

 direction of the length of a spiral shell, and transverse 

 when they cross its breadth. The latter term, how- 

 ever, is not applicable to bivalves, because such marks 



* As is done in the Conchologicnl Manual. 



