I.AMi:i.l.II',KAN\IlI ATA. 



27 



The lines of growth on the risjht valve appear as nnnierous, low and sliarp folds, whilst the left valve, 

 in addition to similar folds, bears in general radially arranged, pored, small vesicles (PI. II, figs, ig — h), 

 the number of which increases towards the peripliery, new ones arising regularly in the interspaces. 



Closer consideration shows, that the vesicles have the lower edge free and that they are .simply 

 outgrowths of the concentric lamellre. Thus, we may find some specimens, in which the left valve 

 in regard to sculpture only differs in the main from the right by some few, distant rows of very 

 small, pocket-like outgrowths (PL II, fig. la), but generally their number is large (fig. ib). Other specimens 

 have larger and fewer, rather \aulted outgrowths (fig. ic). In others again the vesicles are so 

 broad and flat, that they almost meet one another (fig. le). Lastly, we find in the variet}' lamellosa 

 Posselt (fig. if) a form where the vesicles are fused together to concentric, porous wrinkles, formed 

 of projecting, down-turned lamelUe, which at their lower free margin reach to and rest on the next 

 wrinkle; the lamellse are in general interrupted and broken, so that only remnants of them remain as 

 sharp combs. The vesicular outgrowths are also broken off more or less and their position is then 

 shown as a concavity in the line of growth; sometimes almost all the vesicles are rubbed off, so that 

 the lines of growth appear like the cogs on a cog-wheel (fig. id &. li). Among other variations it may 

 further be mentioned, that the upper part of the shell may be almost completely smooth and the 

 outgrowths appear only towards the margin, as shown in fig. 2a; lastly, fig. 2b represents a specimen 

 in which the left valve is almost quite smooth. 



I would not have entered so much into detail on these points had not Prof. A. E. Verrill 

 and Miss Katherine Bush raised these variations to the rank of si^ecies; their I'cctcn piistulosus 

 and P.subiDthrifcr are in fact based on specimens such as are represented in my figures ic and id. 



Distribution, The form major is an arctic, deep-water form (30— 40ofm., perhaps even deeper, 

 650 fm. M, occurring at East Greenland, Jan Mayen and Spitzbergen, in the Barents Sea and the Kara 

 Sea^). The form minor is an Atlantic, deep-water form, which occurs in Davis Strait and off the east 

 coast of the United States of North America, down to ca. 4o°N. L., along West and vSoutli Iceland, S. 

 of the F"seroes and at the western and northern coasts of Norway. The "Thor" has taken it S. E. of 

 the Fseroes (6i"25'N.L., 4°39'W.L., 210 fm.) and in the North Sea (58°32' N.L., 4°i8'E.L., 147 fm.). How 

 far the species goes southwards along the west coast of Europe cannot be stateds), as P.imbrifcr is 

 said not to be identical — as assumed earlier — with the Mediterranean-Atlantic P. Hoskynsi Forb.4). 



Pecten vitreus Chemnitz. 



Pallium vilreuin Chemnitz, Conch. Cab. VII, 1784, p. 335, PL 67, Fig. 637a. — Pccfcn vitreus G. O. 

 Sar.s, Moll. Reg. Arct. Norv., 1878, p. 21, PL 2, fig. 5; Jeffrey.s, Proc. Zool. Soc. 1879, p. 561 ; 

 Smith, ChalL Rep. XIII, 1885, p. 303. — Palliolum vilrcum Verrill, Tran.s. Conn. Acad. X, 



■) St. 192 of the Norvveg. North-Atlantic Exped. lies at 69^46' N.L., i6°i5'E. L., with a depth of 649 fm. and bottom- 

 temp, of — 0.7° C, but I have not seen specimens from here. 



2j Leche's record of its occurrence in the Bering Sea is due to an erroneous determination, as shown on p. 26 note i. 



j) Dautzenberg & Fischer record it right down at the Azores (Dragages effectues par I'Hirondelle et par la 

 Princesse Ahce; Mem. Soc. Zool. France 1897, T. 10, p. 192). 



4) Cf. Dall, Bull Mus. Comp. Zoologj-, XII, 1SS6, pp.214 and 220. 



4* 



