Teller's operculum : revising a rare operculate gastropod from the Silurian of Wisconsin (Laurentia)

• The unique Silurian gastropod with the operculum in place which Edgar E. Teller in 1910 assigned to Murchisonia conradi Hall is redescribed. The date of authorship of Murchisonia conradi Hall, now transferred to Lophospira Whitfield, and originally described from the Racine Formation of Wisconsin (Laurentia), is established as 1865 and not 1867, 1868 or 1870 as variously claimed. With a focus on the operculum, previous studies of Teller's specimen have neglected the form of the shell itself. Latex casts drawn from the external mould motivate its description as a new species, Lophospira telleri sp. nov., and demonstrate that the operculum was positioned deep within the shell aperture. Although being the only proven lophospiroidean operculum, the paucispiral sinistral (in external view) operculum is typical for dextral gastropods of moderate height in which the parietal wall is well developed and the umbilicus narrow. The development of opercula of this type, and the depth of emplacement of the operculum in L. telleri, may reflect increasing predation pressure on gastropods in the Lower Palaeozoic. Suggestions that the operculum of L. telleri may represent the inner surface of an operculum similar to that in the common Silurian euomphaloidean Oriostoma are rejected. In addition to the original record from Wisconsin, isolated opercula of L. telleri are now reported from Thomton Quarry, Illinois.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Annan geovetenskap och miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Other Earth and Related Environmental Sciences (hsv//eng)

Nyckelord

Silurian

operculate gastropod

Lophospiroidea

Laurentia

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