KONGL. SV. VET. AKADEMIENS IIANDL. BAND. 19. N:0 6. 57 



gularly and moderately convex, being most elevated near the median transverse axis. 

 The apex is close to the anterior margin and only very little prominent. The surface 

 of the shell is covered with thread fine ornamental lines parallel to the regular con- 

 centric lines of growth, somewhat interrupted by deeper sulci. It is generally even 

 excepting some wavy, irregular, shallow, longitudinal furroAvs. The aperture is oval 

 with comparatively thin margins, somewhat refiexed outwards. When seen from the 

 side it forms a moderately elevated arch, being highest near the median line of the 

 shell. The central space of the interiör surface is surrounded by an oval ring of six 

 pairs of muscular scars, open anteriorly. The posterior ones are narrow and elongate, the 

 middle ones are transversally broad and much enlarged towards the margin of the shell. 

 The surface of these pairs is smooth or only partially scrobiculated. The uppermost 

 pair is more complicated and consists, as in the kindred species, of a more shallow, 

 elongated interiör portion, and of a larger exteriör one, from the inner corner of which 

 there projects a narrow sinuous groove, directed obliquely upwards and leaving a 

 small, smooth space between itself and the opposite similar one. The lower, interiör 

 part of this upper, muscular scar is pearshaped, wide below, Avith a narroAv, stalklike 

 neck upwards and its surface is finely reticulated by shallow pits and intervening 

 ridges. Some dark, narrow streaks are directed from the enclosed central space of the 

 shell toAvards the interstices betAveen the muscular scars. The AA'hole central part of 

 the shell inside the scars and to their outer edges is of dark colour, Avhile the outer börder 

 is lighter. Near the apex there is on the inside a little oval depression or pit, AAdiich 

 quite resembles a scar, filled up, as if there had been a foramen. But I think it is 

 in reality only the mark of the outlines of the initial shell, Avhere noAv the apex is 

 seen on the outside. The shell is very thin, scarcely exceeding 0,ri millim. in thick- 

 ness and composed of thin, glossy lamellaj, Avhich are not perforated by any parasite. 

 The largest speciraen has been found at Stor Wede in Follingbo and has attained a length 

 of 67 millim., breadth of 51 and height of 15 mill. 



This species has nearly the same geographical distribution as the former. It has 

 been found in several specimens in Fårö at Lutterhorn, Länsa and Norsholm, in Svarfvare 

 huk, the canal near Westöös in Hall, VVestkinde, Häftingsklint, Lummelund, Stor Wede 

 in Follingbo, the limestone cliffs near VVisby and Kyrkberget in Wisby. It has only 

 been found in the strata b and c or the upper and loAver limestone and never in the 

 shale of a. This is rather unexpected as the same species or at least a nearly allied 

 variety, as mentioned above, has been found in the LoAver Silurian strata of Esthonia 

 at Borkholm and also in the Upper Silurian at Koik, in the »Jördensche Schicht». These 

 are only a little more elongate and not so enlarged as the specimens from Gotland. In 

 the Lower Silurian of Canada there occurs a Metoptoma Hyrie, of Avhich BiLLiNGS, Pal. 

 Foss. Canada p. 87, has described a cast Avhich also perhaps on closer examination 

 raay be found to be identical. Met. Erato of the same author, 1. c. p. 39 and Report 

 Progr. Geol. Surve}' of Canada 1863 p. 145, f. 95, can scarcely, as to outAvard shape, be 

 distinguished from the Gotland species, only the distance from the beak to the margin 

 is longer in the Canadian. 



K. Vet. Akad. Ilaudl. Band 19. N:o 0. 8 



