CONCHOLOGY. 77 



Shell irregular, very compressed, foliaceous, sub-equivalve, 

 rather variable form, gaping at the anterior part of the lower 

 extremity ; summit very small, hinge straight, vertical, with- 

 out teeth ; ligament multiple, and inserted in a series of lon- 

 gitudinal parallel furrows. 



Perna ephippium. Perna canina. 



P. obliqua. P. marsupiom. 



P, isogiiomon. P. sulcata. 



P. avicularis. P. vulsella. 



P. femoralis. P. nucleus. 



P.femoralis. The femoral Perna. PI. 14, fig. 1. 

 Species elongated, and with appendages like ears. 



P. vulsella. The tweezer Perna. 



Species elongated, without earlike appendages, or having 

 very small ones. 



P. ephippium. The saddle Perna. 



Species round, compressed, very pearly in the interior; 

 very slightly, if at all, auricled ; margin acute ; exterior pur- 

 plish brown. 



3. Malleus. The Hammer. Six species. 



A shell of a singular form, resembling a pickaxe, found 

 only in the Indian and Australian Seas ; there are two spe- 

 cies, the white and the black, both of which, when in fine 

 preservation, are highly esteemed, but the white is more rare 

 and valuable. 



Shell sub-nacreous, irregular, rugged, sub-equivalve, ine- 

 quilateral, generally auricled before and prolonged behind, 

 so as to be in form like a hammer ; summit entirely ante- 

 rior ; between them and the inferior auricle, an oblique cut 

 or slope for the passage of the byssus ; hinge linear, elon- 

 gated, without teeth ; ligament simple, triangular, inserted 

 in a conical oblique cavity, partly exterior ; one rather large 

 sub-central muscular impression. 



