PLICATULA pectinoides. 

 TAB. CCCCIX.— j%^. 1. 



Spec. Char. Oblong, ovate, curved, gibbose 

 when old ; longitudinal ridges numerous, 

 furnished with depressed spines; free valve 

 externally concave. 



Syn. Placuna pectinoides, Lamarck Hist, Nat: 

 VI.pt. I, p. 224. 



By its curved form, projecting beaks, luiiiierous longi- 

 tudinal ridges, and concave upper valve, this Plicatula 

 is easily recognized ; the spines are not numerous, 

 neither are they regular ; they are always pressed close 

 to the surface, and assist to form the ridges ; it is de- 

 pressed when young, but when old sometimes almost 

 globose ; the length is rarely two inches. 



Collected in Clay, or Gault, below the Chalk Marl at 

 Cambridge, by Professor Sedgwick ; it also occurs in the 

 same formation at Folkstone ; the valves are filled 

 cither with Ironstone or Pyrites. 



Lamarck having seen only imperfect hinges of this 

 shell, from near Metz, has placed it in a Genus it does 

 not at all resemble externally. 



