160 G. LINDSTRÖM, ON THE SILURIAN GASTROPODA AND PTEROPODA OF GOTLAND. 



transverse irabrication dense. The oldest form from the lowest beds of the marly 

 shale of Wisbj^ (Pl. XVII f. 5 — 7) is turbinate, with only three longitudinal keels and 

 a low one around the umbilicus. The ornamentation is for the rest the same. 



This Or. rugosum differs from Or. discors in the more distantiated, transverse 

 laminaj and in their folds being considerably refiexed backwards on the keels. Such 

 a variety of O. discors as that figured pl. XVII f. 1 — 2, connects both. 



3. Oriostoma contrarium n. 



Pl. XX fig. 8—15. 



Shell sinistral, turbinate, with six terete whorls. The apex is sunken and the ex- 

 treme tip is hidden beneath the next whorls, fig. 15. The surface is transversally and 

 obliquely striated by regularly distantiated lameliar ribs, often dividing in two and 

 again uniting, a little wavy in their edge, which is sharp and thin. They are curved 

 sigmoidally upwards towards the umbilicus. The aperture is obliquely ovate or even 

 circular with thin lips and continuous peristome. The inferior part of the exteriör lip 

 is folded in and thus narrowing the aperture. The umbilicus is wide and large. It 

 is defined by a narrow ridge, which is most prominent in young or small specimens, 

 fig. 13, indistinct or only as a swelling in the older. The shell substance is thick, 

 especially in the body whorl. Owing to the different state of pi'eservation the aspect 

 of the surface varies, being corroded in some and only the basal lines of the lamellse 

 left, fig. 14- H. 24 millim., br. 41 millim. Another specimen has in h. 24 mill., br. 

 23 mill. 



It has been obtained from the shale of Wisby, from the limestone beds of Länsa 

 and Lutterhorn in Fårö, Wialmsudd, Samsugn in Othem, the canal of Westöös in Hall, 

 Kyrkberget in Wisby and Hoburg. 



4. Oriostoma glolbosum Schlotheim. 



Pl. XVII, fig. 24, 25, 29—31, pl. XVIII, fig. 24, pl. XX, fig. 16. 



? Valuata sulcata 1776. 

 Delphinula 1811. 



Trochilites globosus 1820. 

 Euomphalus funatus 1823. 



1839. 



1843. 



1848. 



1849. 



1854. 

 1855. 

 1858. 

 1862. 

 1867. 

 1871. 

 1873. 



Walch, der Naturforscher, Neuntes Stiiok, 278, tab. IV f. 5. 



Parkinson Organic Remains, 78, tab. V. f. 18. 



Schlotheim Petrefactenkunde, 162. 



SowERBY Miner. Conch. vol. V, 71, tab. 450 f. 1 & 2. 



Id. Sil. Syst., 626 pl. 12 f. 20. 



Morris Cat. Brit Poss., 144. 



Bronn Nomeiiclator, 479. 



Brown Illustrations of the fossil Conchologv of Great Britain and Ireland, 81, pl. 



XLII figs. 24, 25. 

 Morris Catal. 2d Ed. 248. 

 Mac Coy Pal. Poss., 298. 

 Pe. Schmiijt Geol. Estl., 202. 

 M'CoY Sil. Poss. of Ireland, 13. 

 Salter Sil. ed. 4, 531, pl. 25 fig. 3. 

 Baily Charact. Brit. Possils, pl. 21 f. 9a, 9b. 

 Salter Catal. Cambr. Poss., 90, 157. 



