Homeomorphic gastropods from the Silurian of Norway, Estonia and Bohemia

Redescription of the gastropod Euomphalus undiferus Schmidt, 1858 from the Upper Llandovery Rumba Formation of Estonia requires reinvestigation of the hitherto monotypic genus Kiaeromphalus Peel & Yochelson, 1976, originally described from the Rytteråker Formation of the Oslo Region. The Estonian K. undiferus and the Norwegian type species occur in similar depositional facies of Early Silurian age within the sedgwickii Graptolite Zone. The redescribed type specimen of Horologium kokeni Perner, 1907 from the late Silurian (Ludlow) of Bohemia shows strong morphological convergence with the two Baltic species, but Kiaeromphalus is distinguished by its lower rate of whorl expansion and less oblique aperture. Both genera were adapted to a sessile life, possibly on a soft substratum.