58 N. ODHNER, NORTHERN AND ARCTIC INVERTEBRATES. VI. PROSOBRANCHIA. 2 SEMIPROBOSCIDIFERA. 



of from about 18 to 23 mm. Under these circiimstances the Norwegian form must be 

 considered as iindoubtedly dwarfed as compared with the high-arctic one, 



If the above table is compared with that of V. velutina, it will be found that the 

 whorls in V. undata are one half less tlian those in V. velutina of the same size, and 

 that the aperture in thp present species is usually much more dilated. 



In specimens with an elevated spire (var. zonata) the columella is comparatively 

 narrow; in forma typica (+ var. expansa) it participates in the general dilatation to 

 form a broad concave plate. The reflected columellar margin appears as a fine edg- 

 ing (Fig. 2); at the left side of this recent margin the older ones are visible as lines of 

 growth. The columellar plate is continued on the upper part of the inner wall as a thin 

 calcareous layer connecting it with the outer lip; the peristome is consequently contin- 

 uous, thougli indistinctly so. In elevated forms the increase of the shell is evidently more 

 active in its lower outer part, and the successive positions of the columellar margins 

 may be seen at the left side of the recent one; but in forma typica wliere the depositing 

 of shell substance goes on more actively al) around the aperture, the recent columellar 

 margin falls beyond the older (no traces of them are seen on the plate), and thereby the 

 substance is accumulated, so as to form a sharp crest. By this accumulation the colum- 

 ellar plate becomes somewhat sunken, reminding one of the interiör shelf of Crepid- 

 ula, and in the formation of this lamina the body whorl to some extent participates. 



The consistency of the shell is generally solid; the dwarfed Norwegian forms are 

 more solid than high-arctic specimens of the same size. 



The shell is usually covered with an extremely fine epidermis, often dissolved in a 

 loose velvety coat and sometimes furnished with distinct, though very small and close 

 elevated, crests with fringed edges. Pfeffer (1890) found in some specimens from the 

 Murman coast a cuticula as strongly developed as in V, velutina. 



Variation of the radula. The median tootli in the specimen from W. Greenland 

 figured on Pl. 2, Fig. 1, has a comparatively small cusp and about 5 strong denticles on 

 each side of it. The lateral tooth has a cusp of about the same size and many (about 10) 

 small denticles. A specimen from Bel Sound has a broad median tooth with the margins 

 strongly denticulated (about 6 denticles on each side); the central cusp shows traces of 

 some denticles and its margin is but half as long as the denticulated margin. A radula 

 of the same shape as in V. insculpta is described by Becher (1886) for lus Morvillia grandis 

 (= var. grandis Mörch 1869'' = forma typica). 



General Distribution: 



Norway: Lofoten — Vadsö, 20 — 100 fms, var. zonata (= forma typica of G. O. 

 Särs, 1. 14) and var. expansa (1. 12); Christiansimd, var. zonata {G. O. Särs 1878); Skatören; 

 Kjosen; 30 fms, var. expansa (1. 18, Sparre Schneider 1885); Vardö, in fish stomachs 

 (Sparre Schneider 1894); E. Finmark (Norman 1902),; Northern Norway (Verkriizen 

 1875; Bidenkap 1897). — Murman coast (Pfeffer 1890; Herzenstein 1893). — Russian 

 Lapland (Middendorff 1849). — White Sea; W. coast of N. Zembla; Kära Sea; Siberia 

 (Leche 1878; Aurivillius 1887; Herzenstein 1893); Kära Sea, 10 — 55 m, var. expansa 



