PLICATULA 



the teeth is a small hollow space in each valve, to which is 

 attached the entirely internal ligament. A single, strongly 

 marked, orbicular, muscular impression is observable near 

 the center of each valve. 



Not many species are known ; the recent one of \vhich 

 we have given a representation, is the P. ramosa of La- 

 marck, in his Histoire Naturelle des Anim. sans vert ; why 

 he should have altered its name from gibbosa, formerly 

 established by himself in his S7/sleme^ we know not; we 

 should rather have retained the former name, for if we do 

 not misunderstand the term, ramosa^ as a specific name, 

 conveys the idea of a branched shell, whereas he means it 

 to describe the branched plaits of the outside of the shell. 

 A few fossil species are described, they are characteristic 

 of the Lias. One found near Metz, is engraved in the 

 Encycl. Methodique, and quoted by Lamarck as a Placuna, 

 All those we have seen are more or less closely covered 

 with small spines. 



Fig. I Plicatula gibhosa. 



2 a younger specimen of the same, attached to an Area. 



3 spinosa. 



