The lower Ordovician gastropod Ceratopea

Abstract

Ceratopea Ulrich is interpreted as a gastropod whose description has been based heretofore only on its thickened operculum. Terminology is introduced, predicated on the assumption that the operculum is that of a dextral, low-spired shell. The operculum of Ceratopea is distinguished from that of Maclurites and other opercula occurring in Ordovician strata, by its muscle pit or pits and its peculiar tusklike shape. The orientation in life of the operculum is inferred from its morphology, witti the carina of the operculum being a reflection of the shell periphery. Other generalizations can be made about the shell. Most occurrences of opercula suggest sorting, but six collections of shells and opercula are known. Three of these contain well-preserved pleurotomarian shells fitting the general form inferred from the operculum.A new family, Ceratopeidae, is proposed for pleurotomarian gastropods with thickened opercula. The opercula alone do not furnish clear evidence as to whether the group is monophyletic or polyphyletic. Study of three associations of opercula and shells suggests that these shells are congeneric. From this, it is inferred that Ceratopea is monophyletic, though additional associations of shell and operculum are needed to prove this conclusively. Five species groups are recognized, based on the opercula, but they do not warrant formal taxonomic treatment or rank.Several Ceratopea species are widely distributed geographically and occur within well-defined stratigraphic units; thus, they are valuable guides to interregional correlation. All available geographic and detailed stratigraphic data on all species are summarized. All known species of Ceratopea are figured and described. Of 14 species recognized, 7 are new; 9 formerly named species are placed in synonymy. Ceratopea? pygmaea Stauffer is rejected from the genus but is redescribed.

Ordovician Gastropoda from Northeast Greenland

“…Six are assigned to the same species: Maclurites acuminatus (Billings, 1865), Lophonema taneyensis (Cullison, 1944), operculum and shell of Ceratopea unguis Yochelson & Bridge, 1957, Lophospira aff. perelegans Stauffer, 1937, Turritoma aff.…”

“…Shells probably of C. canadensis occur in the Catoche Formation (Rohr et al 2000. Other shells (not opercula) assigned to the genus include Ceratopea buttsi Bridge, 1957, andC. hami Yochelson &Bridge, 1957.…”

“…Other shells (not opercula) assigned to the genus include Ceratopea buttsi Bridge, 1957, andC. hami Yochelson &Bridge, 1957. Ceratopea canadensis (Billings, 1865) from the Oxford Formation (Cassinian) of Ontario, was illustrated by a line drawing (Billings 1865, fig.…”

“…-Ceratopea unguis is the youngest and most common species of the genus and its operculum expresses the greatest variability (Yochelson & Bridge 1957). The species can be distinguished from C. buttsi Yochelson & Bridge, 1957, by its lack of a sharp carina.…”

“…-Ceratopea unguis is the youngest and most common species of the genus and its operculum expresses the greatest variability (Yochelson & Bridge 1957). The species can be distinguished from C. buttsi Yochelson & Bridge, 1957, by its lack of a sharp carina. The growth lines on the operculum do not necessarily reflect the reentrants along the shell aperture, since the operculum was withdrawn inside the aperture (Yochelson & Bridge 1957, Rohr et al 2004b.…”