LAMELUBRANCH1 VTA. 





The lines of growth on the right valve appear as numerous, low and sharp folds, whilst the left valve, 

 in addition to similar folds, bears in general radially arranged, pored, small vesicles (PI. II, figs, ig 1m, 

 the number of which increases towards the periphery, new ones arising regularly in the interspai 



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

 outgrowths of the concentric lamellae. 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 (PI. II, fig. i a), but generally their number is large (fig. 1 b). < )ther specimens 

 have larger and fewer, rather vaulted outgrowths (fig. ic). In others again the vesicles an 

 broad and flat, that they almost meet one another (fig. i e). Lastly, we find in the variety lamellosa 

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

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

 wrinkle; the lamellae 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 8: ii). 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 Katheriue Push raised these variations to the rank of species; their Pcctcn pustulosus 

 and P. subimbrifcr 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— 400 fin., perhaps even deeper, 

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

 Sea-). The form miliar 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.P., along West and South Iceland, S. 

 of the Faeroes and at the western and northern coasts of Norway. The "Thor" has taken it S. P. <>t 

 the P:eroes (6i°25'N.L., 4°39 / W.L., 2iofm.) and in the North Sea (58 32' N. P., 4 ;, iS'K.P., 147 fm.). How- 

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

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



Pecten vitreus Chemnitz. 



Pallium vitreum Chemnitz, Couch. Cab. VII, 1784, p. 335, PI. '17, Fig.637a. -■ Pcctcn vitreus GO. 

 Sars, Moll. Peg. Arct. Norv., 1878, p. 21, PI. 2, fig. 5; Jeffreys, Proc. Zool. Soc. 1879, P 

 Smith, Chall. Pep. XIII, 1885, p. 303. — Pallidum vitreum Verrill, Trans. Conn. Acad. X. 



■) St. 192 of the Norweg. North-Atlantic Exped. lies at 69 \fy N. I. „ 1" 15 E. I., with a depth ol lid bottom- 



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



2) Leche's record of its occurrence in the Bering Sea is due to an erroneous determination, as shown "ii p 



3) Dautzenberg & Fischer record it right down at the Azores (Dragages effectues par 1'Hiron 

 Princesse Alice; Mem. Soc. Zool. France 1897, T. 10, p. [92). 



i) Cf.Dall, Bull Mus. Comp. Zoology, XII, 1886, i>]> 214 and • 



