108 G. LINDSTRÖM, ON THK SII.URIAN GASTKOPODA AND PTEKOPODA OF GOTLAND. 



Ireland iuid Russia. It is consequently onu of the uiost characteristic Gastropods of 

 tlie Siluriau formation. That thefe sliould be a grcat amouiit of variation in a form 

 of such wide a liorizontal and vcrtical distribution is notbing more than could be 

 expected. As tlie ligiires show, there are elongated and short forms. The variety 

 from Estlionia, tig. 17, is the shortest and more coarsely striated, the body wliorl nearly 

 double the size as tlie others. Its height is 28 millim., its breadth 30 mm. The spe- 

 cimens from the limestone of Slite, ligs. 18, 19, are also short and broad reminding 

 of the Devonian form whieh Hall and Whitfield have called Trochonema rectilatera. 



20. Pleurotomaria qualteriata Schlotheim. 



Pl. XIII liff. 15—16. 



Helicites qualteriatus 

 Solarium .^ pelropolitanum 

 Euompluiltts qualteriatus 



1820. 

 1822. 

 1830. 



1834. 

 1835. 

 1840. 

 1844. 

 1845. 

 1848. 

 1858. 

 1865. 

 1867. 

 1869. 



1880. 



1843. 



1848. 



1854. 



1860. 

 StraparoUus qualteriamis 1850. 



Straparollati pseudoqualteriatus 1850. 

 Rhaphistoma qualteriatum 1859. 



?Ophilela Ottaivensis 1860. 



Pleurotumaria lenticularis 



Euomphalus giialteriatus 



150, tab. I f. 3 a— 3 b, tab. 



ScHLOTii. Petref. Kunde, 103. 



Id. Nafihträge, 61, tab. XI f. 3 a— c. 



Pander Beiträge zur Geogn. Riisslands, 



28 f. 14. 

 GoLDFUss in Klöden, Versteiner. Mark Brandenburgs, 155. 

 Bronn Letli. Geogn. l:e AiiH. Bd I, 94, Taf. II f. 1 a, b. 

 EicHWALU Schichtensyst. Estlands, 115. 

 GoLDFUSs Peti-efacta Gernaaniaj III, 81, tab. 189 f. 3. 

 Veuneuil Eussia, vol. 2, 333, tab. 23 f. 1 a— b, 2 a— b. 

 Salteii Memoirs Geol. Survey II, i, 356, pl. XIV C. 7. 

 Feiedk. Schmidt Geol. Estlands, 206. 

 Kjerule Veiviser, 7 

 TÖRNQDIST Lagerföljdeu i Dalarne, 19. 

 Karsten Versteineruugeu ... iu Sclilesv\dg iind Holstein. 43, tab. 14 



fig. 9 a — b. 

 Angelin & Lindstuöm p. p. Fragmenta Silurica, 12, tab. XV f. 10, 11 



(excl. fig. 12—14). 

 Conrad in Emmons Geol. N. York pt. II, 392 — 393 f. 101,2 & 102. 



Pl. lenticularis Hall Pal. N. Y. vol. I, 172 is quite different. 

 Bronn Nomencl., 480. 



Ferd. Roemer Leth. geognostica ed. 3, I, i, 459, tab. 2, f. 1 a — b. 

 EiciiwALD p. p. Letlisea rossica I, ii, 114. 

 D'Orbigny Prodr. I, 6. 

 Id. Ibid. I, 30. 



S.^LTER Oanad. Organic Eemains, Dec. I, 13. 

 Billings Canadian Naturalist, 166, fig. 9 — 10. 



Shell discoid with short, flat spire of tive and a half whorls. The apieal side 

 is gently convex or nearly flat and the sutures are very shallow. The whorls are on 

 the umbilical side more convex, inereasing in height and convexity near the umbilicus, 

 which is large and open. 



The angle formed by the slit band is interposed between the umbilical and apieal 

 sides and is highly acute, of 30 °. Its limits are designated through the converging 

 threadfine ornamental lines of the surface which for the rest is smooth. The slit band 

 is at largest on the apieal side and there separated from the other surface through 

 no distinct bordering lines. The erescents are fine and indistinct. 



As may be perceived from the dimensions given below, the Gotland mutation of 

 this species is more discoid than the older, which are relatively higher in their last whorl. 



