KONGL. SV. VET. AKADEMIENS HANDL. BAND. 19. N:0 6. 167 



whorls of a screw, giving the outline of the operculum a serrated appearance as shown 

 in the sections 39 & 40. They are directed rectangularly to the longitudinal axis of 

 the operculum or only slightly curved upwards. They are quite sinooth without any 

 smaller, ornamental lines- The dimensions of the operculum are in two specimens: 



A. Height 11 raill. Br. 12. 



B. » 10 » » 14. 



In Martebo almost the same type of operculum has been found detached without 

 any shell pertaining to it. Pl. XVII fig. 36. It deviates, however, in having the coils 

 more distantiated. 



Or. acutum has been found in many fine specimens in a seam of marly limestone 

 at Slita, along with several opercula, of which one m situ. It has also been found in 

 a few specimens at Lännaberget of Slite. 



With an operculum so deviating from that of the other Oriostomata, it raay in- 

 deed be questioned whether this species does not belong to another generic or subge- 

 neric division, what must be left for future researches to decide. 



8. Oriostoma Wislbyense n. 



Pl. XVn f. 26—28, 45—46. 



Shell globular, turbinate, small, of six ventricose whorls. There are only few 

 longitudinal keels, two lai'ger on the apical surface, the lowest leaving a smooth belt 

 between itself and the suture. They are sharp, narrow and prominent, a little jagged 

 by irregular notches. Next them follow at equal distance two smaller keels around 

 the median line of the body whorl and then on the umbilical side a large belt inter- 

 venes, with only faint indications of a few longitudinal lines. Around the umbilicus 

 two large keels leave between them a nearly smooth zone, only finely transversally 

 striated. The transverse strite are gently inclined backwards, somewhat thick, swollen, 

 in other parts fine. All specimens, found in two localities, agree in all particulars and 

 are thus constant in their characters. The umbilicus is wide and deep, showing all 

 whorls. H. 18 mm., br. 18 mm. Spec. B. H. 14 mm., br. 17 mm. 



The operculum, which has been found in situ in one specimen and in several 

 detached specimens, is in the largest specimen of a combined cylindrico-conical shape, 

 being from the base and a while upwards cylindrical, then at the top changing into a 

 conical shape. The inner side is bordered by a rather broad and elevated edge, the 

 enclosed surface smooth, deeply sunk towards the centre, where the whorl is situated. 

 The numerous coils of the outside are more distantiated than in the preceding, with 

 their edges directed upwards. All stria3 decorating them have now disappeared, if 

 once present, and in a section the whorls consequently only show as distantiated, blunt 

 teeth. H. 5 mill., br. 12 mill. One specimen, pl. XVII f. 47, possibly belonging to a 

 different species is elevated and regular, acuminately conical, h. 6 mill., br. 7 mill. 

 From the shale of Wisby numerous opercula have been found, closely resembling those 

 now described, pl. XVII f. 43 — 44, and almost entirely changed into iron pyrites. Their 

 coils are however more thick and less numerous. When seen in a section they are nearly 



