52 N. ODHNER, NORTHERN AND ARCTIC INVERTEBRATES. VI. FROSOBRANCHIA. 2 SEMIPROBOSCIDIFERA. 



General Distribution: 



Norway: Hvitingsö, w. coast; E. Finmark; 30 — 50 fms, 1. 7 (sh.), var. micromphala; 

 Lofoten, Vadsö, among ascidise, 20 — 50 fms, 1. 14 (sli.), var. prodita; Vardö, 30 — 50 

 fms, 1. 8 (sh. ), var. groenlandica (G. O. Särs 1878); E. Finmark, var. prodiia, microin/phala 

 and groenlandica (Norman 1902); Tromsö, var. micromphala (Bergh 1887); Skatören, 

 Lanses and Kjosen, 25 fms, var. micromphala and prodiia (Sparre Schneider 1885'»; Havö- 

 sund, Nordkap, var. prodita (Bergh 1887); Finmark, 30 — 40 fms, var. prodiia (M' Andrew 

 1856). — Off Norway, St. 192, 649 fms, and St. 290, 191 fms, var. 7nicromphala (Friele 

 & Grieg 1901). — E. Spitzbergen, var. prodita (Kraiise 1892). — 81° 1' N. 19° 28' E., 

 180 m, 1 sp., var. prodita (1. an. 22; Knipowitsch 1901''). — White Sea, var. groenlandica 

 (Hcrzenstein 1893). — Sea off Siberia, var. micromphala and groenlandica (Aurivihius 

 1887, Herzenstein 1893). — E. of Iceland, 64° 53' N. 10° W., 600 m, var. micromphala 

 (Friele 1902). — Denmark Strait, 66° 42' N. 26° 40' W., 550 m, var. prodita (Friele 

 1902). — E. Greenland, var. micromphala, 150 — 250 m (Hägg 1905). — W. Greenland, 

 northwards to Egedesminde, var. microinphala; to Proven, 30 fms, var. groenlan- 

 dica, rare (Posselt & Jensen 1899). — E. Canada, M. glahra (Whiteaves 1901). — Massa- 

 chusetts, in fish stomachs under Lamellaria perspicua L. = Oxynoe glabra Couth. 

 (Gould & Binney 1870). Dcptlis 20—649 fms. Clay, sand. 



General Kemarlis on tlie Genus Marsenina. 



Though the above material is not sufficient to give a complete survey of tlie varia- 

 tion, it presents in fact characters connecting the forms described as distinct species 

 (M. glabra, prodita, groenlandica and micromphala), thus showing that tliey all belong 

 to one species, which, according to the rnle of priority, must be named M. glahra (Cou- 

 THOUY 1839). 



Variation. The forms mentioned have been established with regard to the ex- 

 tension of the mantle as well as the form of the shell, and the typical specimens may be 

 arranged in a scheme as follows: 



I. Mantle covering the shell margins only, leaving a dorsal opening of more tlian 

 half the animaPs length uncovered; spirc of the shell low; aperture wide (cfr Fig. 

 7, right) M. micromj^hala Bergh 1853. 



II. Mantle covering more or less of the shell, the central uncovered part of the shell 

 being at most One third of the animaPs length; spire comparatively high; aperture 

 lengthened (cfr Fig. 7, left) I\L prodita (Loven 1846). 



111. Mantle extension unknown; shell with high spire and wide (broad and short) aper- 

 ture M. groenlandica (Möller 1842). 

 The shell has always a reflected columellar margin, continuous with the outer lip; 

 thus, Bergh's original character for M. micromphala, a narrow umbilical slit, is common 

 to all forms of the restored species. 



Transition forms between the above varieties are to be found in the present ma- 



