PANOPiEA. 175 



Panopwa ffJt/cimeris, Bean, Mng. Nat. Hist. vol. viii. p. .'JG'2, f. 50, 51. 

 Pcmopcea arctlca, Gould, Invert. Massach. p. .37, f. 27. — Hanl. Recent Shells, 

 p. 18, suppl. 10, f. 43.— Brit. Marine Conch, p. 38.— 

 Dekav, New York Moll. p. 246. 

 Panopcea Sjxmghri, Valenc. Archiv, do Mus. vol. i. p. 15, pi. 5, f. 3 (not exact). 

 — Chenu, 111. Conch. Panopaja, p. 4, pi. 4, f. 4. 

 " Norvegica, Loven, Ind. Moll. Siiecia% p. Ad. 

 " BivoTKB, Smith, Wern. Mem. vol. viii. p. 107, pi. 2, fig. 4. 



The shape of this interesting shell is oblong, with a 

 slight tendency to be rhomboidal behind. It is extremely 

 thick and heavy, and very decidedly inequilateral. The 

 valves are ventricose, and appear peculiarly so when 

 united, as their edges only touch at the callus near the 

 beaks, and at a point in the ventral margin, which is 

 nearly opposite ; the shell gaping at every other portion of 

 its margin, and particularly at the hinder extremity, Avhere 

 the bending outwards of the edges of the shell increase 

 the hiatus. The outer surface is rather rough, being 

 marked with coarse concentric wrinkles and somewhat 

 obsolete ridges of growth ; but that which chiefly cha- 

 racterises it is the presence of a broad triangular excavated 

 area, which radiates from the beaks subcentrally, and 

 rapidly enlarges as it nears the lower margin. A shal- 

 lower and narrower space runs likewise to the lower 

 posterior corner from the hinder part of the umbones, 

 and thus the intervening surface assumes the appearance 

 of a broad and very oblique obtuse rib, which parts off 

 about two-fifths of the entire surface. The remaining 

 area is nearly equally divided between the impressed 

 triangle and the convex front terminal surface, the sudden 

 posterior cessation of whose convexity makes it appear 

 similarly but not equally like a perpendicularly radiating 

 obsolete ridge, which indeed it is generally described as 

 being, but which, from the si)ecimen before us, we do not 



