ACEPHALA. 31 



any length of time. Besides, it being the object of the 

 conchologist to collect, arrange, and preserve some of 

 the greatest beauties which nature has presented to us, 

 in the form of shells, this object could be effected only by 

 an arrangement founded on the shells themselves. 



Without going further into the general subject of this 

 order, we shall examine a few individuals as types of 

 their general organization, so far as this is known. 



ACEPHALA. 



This term means without head, and common exam- 

 ples exist in the Muscle, Oyster, and Scollop. These are 

 bivalve shells, the two valves being united at the back by 

 a hinge, and connected by teeth which lock into each 

 other. Besides these, the two shells are connected by 



Fiff. 20. 



means of a strong ligament in form of a short pillar, a b, 

 represented in fig. 20, which are the two valves of a spe- 

 cies of [/mo, or fresh water Clam. These ligaments are 

 very distinct in the common species of Venus, called 

 Round Clam, seen in all the fish markets of the Atlantic 

 states. These ligaments hold the two valves together 

 with great force, so that when the animal is alive it is 

 difficult to separate them without a knife. 



There is also in all bivalve shells, a cartilage, gene- 

 rally of a dark color, situated between the two valves 

 at the hinge, the office of which is to force them asunder. 



