146 G. LINDSTROM, ON THE SILHRIAN (iASTROPoDA AND PTEROPODA OF fiOTLAND. 



4. Tr. Stuxbergi n. 



5. Tr. undulans n. 



6. Tr. profundus n. 



7. Tr. cavus u. 



8. Tr. Lundgreni n. 



9. Tr. Kolmodini n. 



II. OARINATI witli longitudinal keels. 



10. Tr. Dalli n. 



11. Tr. Wisbyensis n. 



12. Tr. lamellosus n. 



III. INCISI with angulately impressed suture. 



13. Tr. incisus n. 



14. Tr. gyrans n. 



15. Tr. densestriatus n. 



IV. SPINOSI with spiny processes along the suture. 



16. Tr. astraliiformis ii. 



No species has as yet been found in the Lower Silurian beds of Sweden. 



Div. I. TRANSVERSI. 



1. Trochus Gotlandicus n. 



PI. XIV % 1 — 11. 



Shell broadly conical, sides even, only slightly convex, whorls seven, transversally 

 striated by the oblique, backwards directed, lamellar, wavy lines of growth, which over- 

 lap each other and consequently give the surface an imbricated appearance. They vaiy 

 finer (fig. 1) or coarser (fig. 6). Where the umbilical and apical faces of the last whorl 

 meet they form an acute angle which often is pi'olonged into a horizontal, solid keel. 

 The umbilical surface is nearly flat, smootli, striated by minute, dense lines. The 

 aperture is oblique, almost triangular. The outer lip is thin and sharp, the inner lip 

 reflexed. The umbilicus is closed and there is a marked circular depression around 

 it, defined by a narrow, thread like ridge. The columella is solid. The suture is shallow, 

 often covered by the lamellar keel of the preceding whorls, and the outlines of the 

 different whorls run in a continued profil without any interruption. The apex of the 

 shell is filled up with solid calcareous matter. A peculiar reticulated structure is shown, 

 fig. 9, in thin, transparent cuts of the shell. 



H. 18 mill., br. 35 millim. 



It occurs plentifully at Lansa and Lutterhorn on Far6, in the limestone of Slite, 

 Hall near WestoOs, in the coast all along the shore from Likkershamn to Wisby. A single 

 nucleus has been found in the shale near Wisby and probably belongs to this species. 



