I.AMELLIBRANCHIATA. 1 3 



The largest of these valves is 36 '""'. liigli and 26 """. long-. 



AiuDiig the specimens from Iceland are some down to a size of scarcely 2 """. The prodis- 

 soconch is smooth; immediately under it are radiating ribs, which are more or less spinous and 

 tuberculous. Small specimens are difficult to recognize as belonging to this species, as they are relatively 

 elongated, with the two dimensions of the shell almost the same, and the ears extremely well- 

 developed; they might easily be confused, for example, with the young of Prctot varins. Medium- 

 sized specimens still free are higher than long and of regular form. I^ater, the growth becomes 

 irregular owing to the sedentary mode of life. 



Distribution. In addition to South-West and South Iceland and the Faeroes, P. pusio 

 occurs at Southern Norway, but it has not been found living in the Danish waters inside the vSkaw 

 (a few dead, probably fossil, valves have been taken in the Eastern Kattegat). It also occurs at the 

 British coasts ("on every rocky coast from Shetland to Cornwall"), along the coast of France and the 

 Liberiau Peninsula, through the whole of the Mediterranean right to Asia Minor. It is further distributed 

 as far as INIadeira, Canary Isles, Azores and Liberia, according to Dunker even to the Cape of Good Hope. 



The vertical distribution extends at Norway from o to go fm., according to G. O. vSars, and at 

 the I.ritish Isles from o to 85 fm., according to Jeffreys. Nevertheless, the latter author records the 

 species as taken by the "Lightning" N. of the Hebrides in 530 fm. and b}- the "Porcupine" off the west 

 coast of Ireland in 808 fm. Other authors also record it from great depths, thus Dautzenberg and 

 Fischer') from 1360m. and 1494 m. at the Azores, and A. Locard-) from 896— 2285m. in the Bay 

 of Biscay and north coast of Spain, as also from 1200 m. W. of the Soudan. Is it not possible that 

 these records are based on mistakes? Or were they only dead shells which occurred at the great depths? 



Remarks. Pcctcn piisio is here taken sciisu latiorc. The French malacologist A. Locard defin- 

 itely maintains that the -P-piesio" of the authors covers two distinct species, namely: (i) a free-living 

 species for the whole of its life, of regular form (Pcctcn iiiultistriatus Poll); (2) a species permanently 

 attached in adult condition, always of irregular form (P.distortus da Costa); the first species belongs 

 to the Mediterranean, though exceptionally occurring in the Atlantic as far as the Bay of Biscay 

 and coast of Liberia, whereas the latter species is exclusively an oceanic form, with a distribution 

 from the Azores to Norway J). It seems to me, however, that Lo card's mode of reasoning is not 

 conclusive in the matter. Bucquoy, Dautzenberg and Dollfus seem likewise most inclined to 

 consider P. distortiis and P. vniltistriatus as one and the same species, inter alia^ because both forms 

 ma\- be found as members of the same "colony" and thus in all probability of the same origin. 4) 



Pecten opercularis Linnc. 

 Ostrca opercularis Linnc, vSyst. Nat. ed. 12, i, 2, 1767, p. 1147. — Pcctrii opercularis Jeffreys, 

 Brit. Conch. II, 1863, p. 59, PL 22, fig. 3. 



Pcctcn opercularis Morch, Vidensk. Medd. Naturhist. Foren. 1867, p. 98. 



1) Mem. Soc. Zool. de France, X, 1897, p. 193. 



2) Exped. scient. Travailleur-Talisuiau, Moll. Test. II, 189S, p. 379. 



j) A. Locard: Contrib. a la fauiie nialacol. P'ran(;aisc. XI Monographic. Pecten, 188S, p. 38; idem: Exped, .scient. 

 Travailleur-Talisman, Moll. Test. II, 1898, p. 377—79- 



4) MoUusques marins du Roussillou, II, 18S7— 98, p. 106. 



