KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND. 19. N:0 6. 177 



being of exactly the same size as the aperture. It is of quite the same shape as that 

 delitieated on plate XVII fig. 48. It is tlepressedly conical, of about twelve coils and 

 perfectly circular outline. The coils are large, convex, with the superior border bent 

 out in a thin, laminar edge, the suture between them is shallow. The transverse, oblique 

 strite are distinct. The inside is deeply concave and in well preserved specimens 

 almost all the coils are seen, the outermost forming the elevated borderino- rim. 

 Dimensions: diameter 6 millini., height •') mill., thickness of margin 1 millim. 



In the crystalline limestone near VVesterby in Ardre there occur numerous nuclei, 

 which through some fragments of the shell with its sculpture make it evident that thev 

 have been nearly allied with Cycl. striatum. There seems to have been some varia- 

 bility in the size and distance of the longitudinal, threadlike striae, I'he whorls are 

 six, tubular. Along with these shells, the only ones found there, lie a great number 

 of detached opercula of a type, quite corresponding to that of Cycl. striatum, thoufh 

 modified in details. Its size also tallies with that of the shell. It is figured on plate 

 XXI fig. 66. It is of perfectly circular outline, moderately and obtusely conical. 

 Coils on the outside about twelve, large and broad, proportionately more so than in 

 Cycl. striatum. A little below the upper rim a shallow groove runs. The thin edo-es 

 of the coils are cloven by a narrow slit running along them. The interspace between 

 the adjoining coils is very shallow. The outer sides are ornamented by densely crowded, 

 exceedingly fine and minute, oblique and transversal streaks, reminding of the somewhat 

 larger ones on the outside of the operculum of many of the recent Trochidaj and Tur- 

 ritellida\ On the inside the centre is environed by a thick, callous whorl which en- 

 circles the innermost concavity. Around the whorl the surface is smooth and there is 

 no annular rim. This great dissimilarity of the interior surface indicates a different 

 specific type, which, however, can, for the present, not be succinctly enough described 

 as the shell is so imperfectly preserved. Dimensions of the shell: H. 23 mill., br. 18 

 mill. H. of operculum 5 mill., diameter 11 mill. 



In connection with the forms of opercula, now described, two more may here 

 be mentioned, because they evidently belong to the same generic type. 



1. PI. XVII, fig. 50 — 52. From the lower strata of Ostergarn found in a few spe- 

 cimens. These resemble, as to their exterior, those from Ardre with their large, eight or 

 nine coils which also have a shallow groove running along their superior border. The 

 minute, transverse striiB are not conspicuous and the top of the coils is more lacerated 

 by longitudinal slits. The inner side is also more excavated, fig. 50, and the central 

 whorl not so prominent. An annular rim is formed by the inside of the outermost 

 coil. H. 3 mill., diam. 8, thickness of the margin 1 mill. 



2. PI. XVII, fig. 49. This is acuminately conical, higher than broad, the base 

 is crushed, but it has probably had a circular outline. The coils are broad, band like, 

 ascending like steps, about fifteen. There are indistinct, oblique, transverse lines, nearly 

 parallel with the edges of the coils. A single specimen has been found in the upper- 

 most limestone of Lannaberg in Slite. Diameter 10 mill., height 17 mill. It has to 

 all appearance been still longer- 



K. Sv. Vet. Akad Handl. Bd. 13 N:o 6. 23 



