PANOPiEA. 51 



S. Mcdifcrrnnea fi-oni the Mediterranean, wliich is distin,i>-uisho(I 

 from all the others l»y wanting the eallons snpports of the cartihige, 

 and the S. anstraUH from New HoUand, whicli has the size and 

 streng;li of >S'. borcti/is, and the color of »S'. i'elinn. A notcli in tlie 

 hinge margin lichind the cartihige is also spoken of, which we tlo 

 not fnid in *S'. borailis. It is not a little remarkable that a genus 

 embracing so few s})ecies should be so widely distributed. 



Oeiiiis PANOP.EA, Mexard. 1807. 



Shell eqnivalve, transverse, unequally gaping at the sides and 

 at the base ; a small, conical tooth on each valve, and a rounded 

 callosity at each side to which the ligament is affixed. 



Panopaoa arctica. 



Fig. 27. 



Shell oblong, sub-cylindrical, strong, widely gaping at l)Otli ends, rounded an- 

 teriorly, truncated posteriorly, traversed by two radiating, wave-like ridges, 

 which divide the surfiice into three nearly equal portion.s. 



ilfya Norvegica, Spengl. Skrivt. Nat. Sclsk. ill. 4f>, pi. 2, f^.^,^ IS. 



Glijajmeris arctica, Lam , An. sans Vert. 2d cd vi. 70. — Spengl. Actes do la Soc. d'llist. 



Nat. Copcnh. 45, pi. 2, fig. 18. 

 Pannp(F_a G/i/cymeris, Beax, Mug. Nat. Hist. viii. .5G2, figs .50, .51. — Turt. Br. Biv. 42. 

 Panopca arctica, Gould, Inv. 1st ed. 37. — Haxley, Rec. Sh. 18, Suppl. 10, fig. 4."5 ; Br. 



Mar. Conrh. .38. — De Kay, Nat. Hist. N. Y. 246. 

 Panoprra Spcnijleri, Valenc. Arch, du Mus. i. 15, pi. 5, fig. .3 (pour). — Ciienu, 111. 



Conch. (Pan.) 4, pi. 4, fig. 4; Man. de ronch. ii. 27, fi- 118. 

 Panopira. Norri'i/icn, Lovfe.v, Iiid. Moll. Scand. 49. — Fordes and Hanl. Br. Moll. i. 



174, pi. 11, pi. w. (anini.) Suppl. — Woodward, Pr. Z. S. 220 (1855). — Adams, 



Gen. ii. .351, j)!. 94, fi>is. .3 3 <(, 3h (anim.) — Middend. Sihcr. Reisc (Moll.) 109; 



INIalac. Ross. pt. iii. 77, pi. 20, fig. 11. 

 Sa.ricava Nnrvrgicn, Woodw. Man. of Moll. 319 (1851) ; Proc. Z. 8. 220 (1855). — Mol- 



LER, Moll. Grcienl. 18. 



Shell thick and strong, oblong, somewhat cylindrical, inequilat- 

 eral, the posterior portion being nearly twice the length of the ante- 

 rior ; somewhat acutely rounded before, obliquely truncated, and 

 widely gaping behind, the posterior margin thickened within, and 

 turning outwards; the hinge and basal margins are usually about 

 parallel, Ijut in old shells the lower and posteriiir angle is consid- 

 erably prolonged, so as to render this portion broadest, and it is 

 the only point at which the valves meet, the rest of i\\Q base widely 

 gaping; beaks rather prominent, directed slightly forwards, and 

 from them extend two broad, wave-like ridges, one directed to the 



