21 
FRODU CTU S hiimerosus. 
TAB. CCCXX1I. 
Spec. Char. Oblong, squareish, depressed, 
striated, spinose? or hispid? hinge line less 
than the width of the valve ; in the larger 
valve are two very deep cavities near the 
beak, and a third connected with the beak ; 
front flatfish. 
As no other indications of this species than casts re- 
main, the existence of spines and strise upon it, can 
only be inferred from the punctmns which are arranged 
in irregular rows upon the cast of the larger valve : the 
protuberances that correspond to those cavities which 
are distant from the beak, are blunt cones ; while that 
which filled the beak is obscurely divided into four lobes, 
and bears a slight resemblance to a head between two 
high shoulders, as the name implies. The length rather 
exceeds the width. 
From Breden, near Derby, by favour of the lamented 
S. Tennant, Esq. ; the same specimen is figured in my 
British Mineralogy, tab. 217, as an example of Magne- 
sian Limestone in which it occurs. 
