KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 50- N:0 5- 69 



General Distribution: 



Norway: the whole coast to Vadsö, 8 — 200 fms (1. 8, forma typica, 1, 12.5, var. 

 cryptospira; G. O. Särs 1878); E. Finmark, type and var. (Norman 1902); Skatören, 

 20 — 30 fms, on Cyntliia, type (1. 9; Sparre Schneider 1885); Finmark, 10 — 40 fms (Mc 

 Andrew 1856); Bergen (Friele 1874); Christianiafjord, 8 — ^10 fms, Laminarise (M, Särs 

 1870). — Bohuslän: Stångholmsrännan, Gullmarn, 20 fms (Malm 1855, Théel 1907). 

 — Denmark: Hellebsek, 16 fms (Mörch 1871; Petersen 1888). — Belgium, very rare 

 (Maitland 1897). — E. coast of England and Scotland from Scarborough to Orkneys 

 and Slietland; Hebrides and W. of Scotland (Jeffreys 1870; Hargreaves 1910); Slietland 

 — Faroes, 160 m (Simpson 1910). — Faroe Islands (Mörch 1868). —Zeeland (Mörch 1869=*); 

 D:o, Adelvig, 5 'A, fms, var. cryptospira (Posselt & Jensen 1899). — White Sea (Herzen- 

 stein 1893). — Behring Sea, var. cryptospira: St. Lawrence Island (Aurivillius 1887); 

 Norton Sound; Pribiloff Islands; Aleiitians; Sitka (Dall 1875); Commander Islands (Dall 

 1887). — Sea of Ochotsk; Schantar Island, var. cryptospira (Middendorff 1849, 1851; 

 Dunker 1882). — Off Halifax, Newfoundland, 57 fms, 1 living sp., var. cryptospira (Whi- 

 teaves 1901). Deptlis to 200 fms. Clay, sand, stones. 



General Remarks on the Genus Yelutina. 



In the above account it has been pointed out in wliat a manner the variation finds 

 expression within the separate species. In the following pages a comparative survey 

 will be given of the formation of so me of the organs within the genus, 



The shell in V. velutina is calcareous with a well-developed cuticula; this may, 

 however, be somewhat reduced (var. Schneideri). In V. undata it is calcareous with 

 a very thin or feeble cuticula. In V. lanigera on the other hand a reduction of the cal- 

 careous layer takes place, which is carried on fujther in V. plicatilis; even here, how- 

 ever, a calcareous embryonic shell is always retained. Also the nnmber of whorls, in all 

 the species, is reduced in relation to V. velutina, which in this respect as well as from other 

 characters may be regarded as the most primitive of all. The peristome is continuous in 

 all species, though this character is but feebly marked in V. undata. By that cir- 

 cumstance as well as by the forms with a narrow columella (V. insculpta) and a niem- 

 braneous or otherwise well-marked cuticula, the last species is connected with V. velu- 

 tina, just as V. plicatilis approaches the same species owing to the formation of the cuti- 

 cula and the calcareous layer in the Siberian specimens. 



Under such circumstances, as the species owing to their extensive variations are 

 difficult to keep distinct, a further subdivision, as was proposed by Gray 1847 on the 

 strength of the shell characters, has no justification. In the following pages fm-ther 

 proofs will be found addiiced to show that the species even in the soft parts mark con- 

 fluent stages of reduction or development from the conditions typical for V. velutina. 



The shell muscle is attached both to the columella and to the interiör of the aperture, 

 on its upper and its lower walls. The muscle forms a semicircle around the posterior 



