KONGL. SV. VKT. AKADEMIENS IIANUL. liANI). |9. N:0 6. 105 



Shell largely conical, trochiforin, with ten gently convex whorls, angular at the 

 shallow suture where the slit hand is placed in the older whorls, being median in the 

 free body whorl. It is comparatively large, with a longitudinal ridge above the middle 

 line, not far from the superior border. This, however, as may be gatliered from the 

 figures 10, 12, 14, varies, the ridge being nearest the central line in specimen fig. 14, 

 wliicli is from the Lower Silurian of Oland at Lerkaka, and more prominent than in 

 any one of the others. In specimen figure 10, the ridge of the slit band is placed 

 nearer to the superior border than in the others and is only ver}' little prominent. 

 The crescents are consequently more or less oblique, as their greatest curve coincides 

 with this ridge. They are densely set, fine, thicker at the ridge and thinning out 

 towards tlie borders. The surface on both sides of the ridge is a little scooped out, 

 as seen in the profiles delineated. This median ridge does not, however, continue all 

 the way round, but ceases in the vicinity of the aperture, as seen in fig. 10, upper 

 detail, where the large slit band is only obscurely hemmed in by bordering lines and 

 covered with regularly curved crescents. The slit is angular, tongue shaped with evenly 

 curveil sides. On the nucleus the slit band has made an impression as a shallow 

 groove. The thin shell which seldom is preserved entire, is covered by fine stria-, 

 which meet the slit band as usual in a liighly acute angle. At their basis, near the 

 suture they are more apart and form band like plaits. The aperture is transverse, 

 with the exterior lip thin and sharp and the interior lip regularly reflexed, but not 

 so mucli as to hide the narroAv and open umbilicus. Length 30 millim., breadth at 

 tlie basis 26 mill., apical angle 71 °. 



Only two specimens have been found in Gotland; one, fig. 10, in a detached 

 block from the Norderstrand near Wisby, the other, fig. 12, from Ostergarn. As to tlie 

 derivation of the former, it is questionable whether it really has been included in a 

 Gotland rock and rather not has been found in an erratic block, of which some, spread 

 over Gotland, contain Lower Silurian fossils. The specimen from Ostergarn seems 

 indeed, to judge from the rock, to have been found in the Upper Silurian strata of 

 that locality. 



There cannot be any doubt that this species is the same as tliat so named b}' 

 IIisiNGER. The original specimens of this author are contained in his own collection, 

 now in the I'aheontological Department of the Swedish State Museum and consist of 

 two badly preserved nuclei from Dalecarlia, without any traces left of tlie shell. One of 

 them, a little compressed from the sides, is the original specimen to his figures in 

 »Anteckningar» pt. 5, two af which have been copied in the MLetha-a Suecica». Later, 

 several complete specimens have been found in strata of Oland, contemporaneous 

 with the former. As can be seen on the plate VIII to this work, fig. 14, the Oland 

 specimen has only trifling deviations in the character of the slit band, such as only 

 can be expected in a species of so wide a geological range. There exists then, as 1 

 suppose, no necessity^ to subdivide this species into new ones, as some later authors 

 seem inclined to do by always citing "Plenr. ellipt.ica His. sp." There may at the 

 utmost be mutations. The oldest known mutation is from the Upper (u-ay Orthocera- 



K. Sv. Vi't.-Aknd. Hiiiirtl, H.l. l:i. N:o G. 14 



