206 MULTIVALVES. 



Though dissimilar in their appearance, these 

 shells are united by many points of resemblance ; 

 they are all more or less of a conical form, com- 

 posed of several valves, and are parasitical. The 

 animals inhabiting them are very similar, and 

 differ much from other mollusks. They have 

 no head or eyes, the mouth has jaws, with horny 

 laminae or erect teeth ; but the most singular 

 part of their structure consists in the numerous 

 tentacular, curled, articulated arms; these vary 

 in number, some of the species have as many as 

 twenty-four. They are arranged in pairs, and 

 are all inserted together ; the twelve longest are 

 erect and arched, appearing like curled feathers ; 

 they are clear and horny ; each joint is furnished 

 with two rows of hair on the concave side. The 

 animals make use of these organs to catch their 

 prey, and are continually extending and con- 

 tracting them. The twelve smallest are placed 

 in front, they are more flexible, and more thickly 

 set with hairs than the others. 



The sessile shells * are now formed into a dis- 

 tinct genus called Balanus: they adhere imme- 

 diately to marine substances at their base, and 

 remain immoveably fixed for life ; the form of 

 the shell is conical, and the valves of which it 

 is composed, are so strongly cemented as almost 

 to appear like a single piece. From the con- 

 struction of the shell, its immoyeable walls, and 

 its large opening at the apex, the animal would 

 be in a very exposed and perilous situation, 



* Plate X. figure 6. 



