KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND. 19. N:() 6. 107 



central axis, is uear the suture swelling in a, iiarrow obtuse ridge, the median face 

 is parallel to the axis of the shell, and the superior one is inoderately convex sloping 

 outwards. The median face is coniined within the characteristic two longitudinal rid- 

 ges, which are more or less prominent in the different specimens. Of these ridges 

 the largest or second one from above is the slit band, as may be learned through a 

 closer inspection and by the direction of the ornamental stria; of the surface on each 

 side of it. As seen in the figures, especially in fig. 23, it is distinctly separated from 

 the other surface by bordering lines. It is formed on the same plan as in the pre- 

 ceding species, of oblique, dense crescents, the obliquity of which is influenced by the 

 position of the longitudinal ridge. This ridge varies as to its position more than in 

 any other species of this division, being placed in the middle of the band (fig. 19, 21) 

 or near the superior börder (iig. 22) or quite on the contrary near the inferior börder 

 (fig. 23). Its variations as to the size may also be perceived from inspection of such 

 extremes as figs. 19 and 22. 



The surface is densely covered by transverse, fine, elevated stria^, which are 

 directed backwards from the suture in an elegant curve. Above the slit band they 

 continue nearly vertically and again above the uppermost ridge curve backwards. 

 There is some variation as to their fineness and proxiraity, of which figures are given. 

 From Gothemshammar there is a peculiar variety (figs. 24 — 25) agreeing in all par- 

 ticulars with the described specimen, but being provided with a ridge beneath the slit 

 band, midway between this and the suture. The aperture is elongated, nearly twice 

 as long.as broad, the exteriör lip angular, thin and sharp, the inner lip reflexed in a 

 large, smooth fold, which is often scooped out longitudinally and entirely covers the 

 umbilicus. 



The nucleus is strangely globose in the older whorls, only angular in the body 

 whorl, and a thin covering of a nacreous stratum is left behind on it. 



Dimensions. Largest specimen 65 millim. in height, 35 mill. in breadth, apical 

 angle 62 °. Height. Breadth. Apical angle. 



Specim. fig. 15 45 mm. 33 mm. 78 °. 



— 18 45 » 39 » 87°. 



— 24 10 » 6 » 62°. 



By this and many other instances may be found how little reliance can be put on the 

 size of the apical angle as a specific character. This beautiful and characteristic shell 

 bas been found in several specimens in many localities of Gotland, in Fårö at Länsa, 

 at Slite in the shale beds and the superimposed limestone, Gothemshammar, Östergarn, 

 Ardre, Samsugn in Othem, Martebo, in the limestone of Wisby, at Stor Wede in Fol- 

 lingbo, Krokstäde in Tofta, Westergarn, Djupvik in Eksta and in a section between 

 Stjernarfve and Lefvede, on the shore of Kylley, in the canal near Atlingbo church. 



This species has a geological range from the Lower Silurian strata of Borkholm 

 in Esthonia, through the Upper Silurian into the Upper Helderberg strata of the 

 Devonian group. Turbo bicingulata F. A. Roemer Pala?ontogr. vol. 3 pl. V fig. 20 

 from the Devonian of the Harz mountains is probably also identical. Its geographical 

 distribution is equally wide, as it besides Sweden occurs in N. America, Scotland, 



