PANOP.EA. 51 



S. Mediterranca from the Mediterranean, which is distinguished 

 from all the others by wanting the callous supports of the cartilage, 

 and the S. australis from New Holland, which has the size and 

 strength of S. borca/is, and the color of S. velum. A notch in the 

 hinge margin behind the cartilage is also spoken of, which we do 

 not fmd in S. borcalis. It is not a little remarkable that a genus 

 embracing so few species should be so widely distributed. 



Genus PATVOP.*:.!, Menard. 1807. 



Shell equivalve, 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. 



Panopsea arctica. 



Fig. 27. 



Shell oblong, sub-cylindrical, strong, widely gaping at both ends, rounded an- 

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

 which divide the surface into three nearly equal portions. 



Mya Norregica, Spengl. Skrivt. Nat. Selsk. iii. 46, pi. 2, fig. 18. 



Gli/cijmeris arctica Lam , An. sans Vert. 2d ed. vi. 70. — Spengl. Actes de la See. d'Hist. 



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

 Panopn^a Gljjcijmeris, Bean, Mag. Nat. Hist. viii. 562, figs 50, 5L — Tcrt. Br. Biv. 42. 

 Panopcea arctica, Gould, Inv. 1st cd. 37. — Haxley, Rec. Sh. 18, Suppl. 10, fig. 43; Br. 



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

 Panopcea Spengleri, Valexc. Arch, du Mus. i. 15, pi. 5, fig. 3 (poor). — Chexu, 111. 



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

 Panopa>a Norrrgica, Lovix, Ind. Moll. Scand. 49. — Forbes and Hanl. Br. Moll. i. 



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



Gen. ii. 351, pi. 94, figs. 3 3«, 36 (anim.)— Middend. Siber. Reise (Moll.) 109; 



^lalac. Ross. pt. iii. 77, pi. 20, fig. 11. 

 Saxicuva Norvegica, Woodw. Man. of Moll. 319 (1851) ; Proc. Z. S. 220 (1855). — MoL- 



LER, Moll. Groenh 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, but in old shells the lower and posterior 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 the base widely 

 gaping ; beaks rather prominent, directed slightly forwards, and 

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



