12 - Conchology. 



Hinge, the point of union between the two valves, formed 

 by the connection or articulation of the teeth in both valves, 

 or by the teeth in one valve fitting into hollows or sockets in 

 the valve opposite, fig. 8, h. 



Byssus, the appendage called the beard ; by means of 

 which some bivalves fasten themselves to the rocks. 



Mlltivalves. The shells of this order are few, compared 

 with either of the preceding ; and the terms proposed for 

 those, are applicable for the most part to the multivalves. The 

 following require more explicit mention. 



Z?ase, that part of the shell upon which it rests: in the lepas 

 tribe it implies the part immediately seated upon the stem or 

 pedicle; in the balani, the base is generally larger than the 

 summit, and is the bottom by means of which the shell is fixed 

 upon the rocks or other extraneous bodies, fig. 10, a. 



Ligament, the substance, whether membranaceous or tendi- 

 nous, w hich serves to connect the valves together. The con- 

 nection of the valves in some multivalves is formed by the 

 parts of one valve locking into another, fig. 11, v, v. 



Operculum. The balani have the aperture at the summit 

 closed by means of four small pieces of valves, which are 

 commonly called the operculum; these opercula of the balani 

 are, however, very different from those of univalve shells, fig. 

 10, o. 



Such are the general terms applied to the parts of shells. 



The animals uhich inhabit shells are classed in the grand 

 division Mollusca of Cuvier. In this division the sentient prin- 

 ciple is lodged in a number of medullary masses, dispersed in 

 different parts of a soft body. And though the medullary masses 

 are not always united by nervous filaments, the organs of sense 

 and motion are arranged more or less on two sides of a nervous 

 axis or longitudinal series of medullary masses. 



The principal medullary mass is situated upon the throat. 

 The circulatory system is considerably complicated ; much 

 more so than that of the articulated division. The blood is 

 dark-colored or blue. Fibrin appears more abundant than in 

 vertebral animals. Their muscles are attached to many parts 

 of the skin, forming a tissue more or less complicated and 

 compact. By various contractions and elongations they 

 move, swim, and perform other motions. They have consid- 

 erable irritability ; the naked skin is very sensible and fur- 

 nished with a liquid humor which issues from its pores. 



Molluscous animals are likewise arranged into classes, 

 orders, genera, species and varieties, a full account of which 

 cannot be given in the small extent allotted to this work. 



Mv 



