KONGL. SV. VET. AKADEMIENS HANDLINGAE. BAND 19. N:0 6. 169 



mill. This is the cominon proportion, but in a few instances the shell is so much 

 elongated, as to be higher, thaii broad, fig. 25, h. 40 milL, br. 34 mill. 



Of the operculum of this species the State Museum in Stockholm possesses three 

 specimens in situ, of which two are too fragmentary for description. In one shell 

 there is the impression of the interiör side on the nucleus. A cast in plaster of Paris 

 shows that this side nearly resembles that figured on plate XVII fig. 35, the central 

 whorl being larger, the marginal rim flattened and the central concavity not so deep. 

 It is probable that the outer side, which is not preserved in any specimen, also re- 

 sembles that of Or. globosum. 



This species is very common and is indeed the most characteristic one in the 

 shale beds around Wisby and also in the overlying limestone. A few specimens 

 have also been found in the shale beds of Gnisvärd and Westergarn, proving the con- 

 temporaneity of these strata with those of Wisby. There are also single specimens 

 from the upper and lower strata of Hallshuk. 



Or. Roemeri, which easily might be confounded with some of the varieties of 

 Or. sculptum, differs from them through the continuity of the longitudinal ridges close 

 to the suture, while they are somewhat more distantiated in the låter and there is a 

 space left free without any revolving lines between the lowest keel and the suture. 

 The umbilicus is narrow in Or. Roemeri, wide and open in O. sculptum and environed 

 by two higher ridges, while in Or. Roemeri all ridges are of the same size. 



Besides the opercula, which with absolute certainty can be referred to the prece- 

 ding four species or are most nearly related to them, there are some others which 

 belong to unknown species of other genera, also unknown, but probably of the same 

 faraily. They may be described here in connection with the former. 



1. Pl. XVII fig. 53 — 55. Four specimens of this variety have been found in 

 the middle limestone beds of Wisby. They are regularly circular, depressed, nearly 

 flat, thin, attaining their largest thickness around the borders and at thinnest in the 

 centre. Section fig. 54. The coils on the outside are rather irregular or, as it were, 

 occasionally evanescent, thick and coarse around the margins, narrower and more indi- 

 stinct near the centre. The marginal coils are obscurely ornamented by finer, con- 

 centric lines. On the inside, which is shallow and concave there is no elevated annular 

 rim as in the preceding type, the whole surface is sloping without interruption, smooth 

 and glossy, to the centre, where a broad, faintly distinguished whorl is seen. Diam. 

 13 millim., thickness of margin 2 millim. 



2. Pl. XVII fig. 56. A single specimen with the inside affixed to the rock has 

 been obtained from Samsngn in Othem. It is of obovate outline, flat, the numerous 

 coils are coarse and angular. A section, fig. 56, reveals that they are narrow lamells, 

 inwards bent, at largest near the margin and diminishing towards the centre. It is 

 thickest along the margin. Longest diameter 18 millim., the shortest one 15 mill., 

 thickness at the margin 2 millim. 



3. Two specimens from the upper limestone of Hogrän. The outline is obo- 

 vate, the outer side, the only one accessible, is entirely flat, without any prominence 



K. Vet. Akad. Handl. Band 19. K:o 6. 22 



