146 o. LINDSTRÖM, ON THE SILURIAN GASTROroDA AND PTKROPODA OK GOTLAND. 



4. Tr. Stuxbergi n. 



5. Tr. undulans n. 



6. Tr. profundus n. 



7. Tr. cavus n. 



8. Tr. Lundgreni n. 



9. Tr. Kolmodini n. 



II. OARINATI with longitudinal keels. 



10. Tr. Dalli n. 



11. Tr. Wisbyensis n. 



12. Tr. lamellosus n. 



III. INOISI 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. astraliiforinis n. 



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



Div. I. TRANSVERSI. 



1. Troclius Gotlandicus n. 



Pl. XIV fig. 1—11. 



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

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

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

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

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

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

 aperture is oblique, almost triangulär. 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 lameilar 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 plentifnlly at Länsa and Lutterhorn on Fårö, in the limestone of Slite, 

 Hall near Westöös, 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. 



