10 N. ODHNER, NORTHERN AND ARCTIO INVERTEBRATES. VI. PROSOBRANCHIA. 2 SEMIPROBOSCTDIFERA. 



A. Secondary inantle börder forming a swelling under the shell margin, reflected 

 Tipon the shell or not; a distinct inspiratory and an indistinct expiratory fold 

 on its under-side. Shell entirely exteriör (sometimes partly covered by the 

 secondary mantle), distinctly spirally twisted Velutina Fleming 1822, 



B. Secondary mantle entirely covering the shell, its börder forming a blunt ridge 

 encircling the foot, with distinct inspiratory and expiratory folds. Shell 

 membraneous, flattened and shield-like withoiit spire 



Onchidiopsis Bergh 1853. 



Ltamellaria Montagu 1815. 

 Marsenia Leach 1820. 



T. Outer mantle tuberciilated, usually grayish with black stripes and yellowish döts; 

 spire somewhat elevated with impressed suture; aperture 3 — 4 times as long as the 

 breadth of the columellar margin; length of the shell < twice its height, when rest- 

 ing on the aperture; outer lip, seen from spire, inserted angularly to the body whorl. 

 L. 18 — 27 (animal), 11 — 18 (shell) mm L. perspicua (Linné 1758) 



(== L. producta Leach 1847). 

 Pl. 1, Figs. 1—5. 

 II. Outer mantle nearly smooth, brownish with darker brown spöts; spire flattened; 

 aperture 4 — 5 times as long as the breadth of the columellar margin; shell more de- 

 pressed than in the preceding species, its length > 2 times its height; outer lip, as 

 seen from spire, almost evenly passing into the outline of the body whorl. L. of 

 shell about 9 mm L. latens (Muller 1776) (= L. tentaculata Montagu 1811). 



Pl. 1, Fig. 6. 



Marseiiiella Bergh 1886. 



Outer mantle coarsely and finely graiiulate, of a yellowish colour with liglitcr döts and blackish clouds; 

 shell of a horny yellowish colour with scattered traces of a thin calcareous layer on the inner surface of the 

 spire. L. of the animal 22, br. 15, h. 11 mm; L. of the shell 13, hr. 10, h. 5 mm M. borealis Bergh 1886. 



Marseiiiiia Gray 1850. 



Shell with a more or less elevated spire, opaque white, fragile, covered with an ex- 

 tremely thin hyaline cuticula; secondary mantle edges reflected and more or less expand- 

 ed över the shell, white or reddish coloured with reddish brown spöts. L. of the animal 

 about 17 and of the shell about 10 mm M. glabra (Couthouy 1838)'. 



Pl. 1, Figs. 7—11; Pl. 5, Figs. 30, 31. 



Telutiiia Fleming 1822 2. 



incl. Limneria H. & A. Adams 1853 (= Morvilha Gray 1857) and Velutella Gray 1847. 



I. Shell entirely calcareous with a very feeble (or no) cuticula, usually of a downy 

 appearance owing to close fine elevated spiral lines; shell sculptured with extremely 



^ For the varieties see the general remarks in the geographical section. 



2 The suhdivision is based upon tlie results of the general investigations on the genus, publishcd in the 

 geographical section of this work. 



