40 



INTRODUCTION. 



separate valves, placed in a longitudinal series, being joined to 

 each other by inserted lamina, and named Articulata by De 

 Blainville, on that account. The genus Chiton is the only 

 example of this kind of Multivalves. 



Fig. 84, 85, Chiton, a, anterior ; j», posterior ; d, dorsal ridge ; 1 1, lateral 

 areas of the valves ; c c, central areas j i i, inserted lamina ; m, margin. 



The second kind, not shells of true Mollusca, M. De 

 Blainville terms the lateral bivalves, the pieces being placed 

 in pairs on each side of the animal; these compose the 

 " Pedunculated Cirripedes," or Lepadse. 



Pig. 86, Lepas. a, peduncle ; h, cavina ; c, scutum ; d, tergam ; e, cirri. 



They differ considerably in the number and arrangement of 

 the valves ; the small ones, which are found near the peduncle 

 in some species, are sometimes termed accessary valves ; those 

 which form the edge through which the bunch of Ciha pro- 

 trude, are termed ventral, and those on the opposite side 

 dorsal. The extremity joining the peduncle is the basal, or 

 anterior ; and the upper extremity is the apicial, or posterior. 



The third kind are termed coronular by De Blainville, and 



