52 



SOLENID^. 



Fig. 373. 



lower posterior angle, the other dividing the portion anterior to 

 this into two nearly equal parts, so that the surface is thus divided 



into three triangular, con- 

 cave compartments ; sur- 

 face also ridged at the 

 lines of growth. Di- 

 rectly under the beak 

 in each valve is a single 

 small, triangular tooth ; 

 these shut side by side ; 

 running backwards from 

 each of them, along the 

 margin, is a thick, round- 

 ed, crest-like callus, hav- 



Panopcea arctica. 



ing a groove at its exter- 

 nal base in which a strong ligament is fixed, which arches over 

 these crests. Muscular impressions deep ; pallial impressions look- 

 ing like an irregular series of muscular pits of various sizes ; inte- 

 rior smooth and shining, corresponding to the external undulations ; 

 exterior antiquated, livid, covered with a thick, dusky epidermis, 

 wrinkled posteriorly. Length, two and one half inches ; height, 

 one and three fifths inches; breadth, one and one tenth to one 

 and six tenths inches. 



Inhabits the jjanks of Newfoundland, whence it is 1)rought by 

 fishermen. Tliroughout the arctic seas from Behring's Straits to 

 Newfoundland, the North Sea, and Russian Lapland ( Woodward) ; 

 Arctic Seas of Europe (Middend.) ; dredged in Bedford Basin, Hali- 

 fax (^Willis) ; taken (dead) in forty fathoms. Grand Manan (^Stimp- 

 son) . 



I believe this to be the shell which Lamarck intended by his 

 Glycymeris arctica^ and which Deshayes, with good reason, pro- 

 nounces to 1)0 a Panop^a. I am aware that the P. Aldrovandi 

 varies much at different ages, and has consequently lieen described 

 under several names. It is also said to l)e an inhalntant of New- 

 foundland, while Lamarck gives the "Arctic Ocean, the White Sea," 

 as the habitat of P. arctica. But P. Aldrovandi never presents 

 upon the disk the two ridges and intervening central valley, so 

 characteristic of our shell, it is also nearly equilateral, broadest 

 before, and the anterior extremity is scarcely more rounded than 

 the posterior, and, even at the immense size to which that species 

 often arrives, it is scarcely more thickened than our small sliell, 



