149 



PERNA quadrata. 



TAB. CCCCXCII. 



Spec. Char. Quadrilateral^ one side shorter than 

 the other three ; valves gibbose, unequal, the 

 shorter side very concave, bounded by two 

 obtuse carinae ; beaks prominent. 



A KEMARKABLY square and convex Perna ; the crena- 

 tures in the hinge line, which fills one of the sides, are 

 few and large. The shell, to judge from the remaining 

 portion of the spar that filled the space it once occupied, 

 was very thick, and so concave on the side beneath the 

 beaks as to form there a heart-shaped cavity, bounded by 

 ridges that curve gently along the beaks : in the centre 

 of this cavity it is probable the byssus passed : the beak 

 of the larger valve projects a good deal, the other is 

 shorter ; they are both pointed, and nearly straight. 



This is little more than a cast in compact Limestone 

 containing a little Mica ; but as the characters are very 

 conspicuous, and as it is probable the outside will not 

 easily be detached from the stone when other specimens 

 are found, we have not thought it necessary to postpone 

 the figure. 



It is from the Cornbrash at Bulwick, and was found 

 by John Hogg, Esq. 



