MOLLUSCA FROM THREP: HUNDRED FATHOMS — -HEDLEY. 225 



and disposed in radiate and concentric lines. Interior brilliantly 

 pearly, the muscle scars indistinguishable in our specimen. The 

 inner ventral margin faintly minutely crenulated. Length 5-5 ; 

 height 4-8 mm. 



This appears to most resemble P. cymata, Dall,'' from the west 

 tropical Atlantic, than which it seems to be shorter, with a more 

 feeble and oblique fold. 



Two odd valves from two hundred and fifty fathoms, and 

 fragments of larger specimens from three hundred fathoms. 



Dall- Proc. U.S. Nat. Mus., xii., 1889, p. 289, pi. viii., f. 4. 



