5 
PLICATULA pectinoides. 
TAB. CCCCI X.—Jig. 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 . 1, p. 224. 
By its curved form, projecting beaks, numerous 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 Mar! at 
Cambridge, by Professor Sedgwick ; it also occurs in the 
same formation at Folkstone; the valves are filled 
either 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. 
