Glabrocingulum Thomas, 1940

Foster, William J., Danise, Silvia & Twitchett, Richard J., 2017, A silicified Early Triassic marine assemblage from Svalbard, Journal of Systematic Palaeontology 15 (10), pp. 851-877 : 866

Genus Glabrocingulum Thomas, 1940

Type species. Glabrocingulum beggi Thomas, 1940 ; Carboniferous , Scotland .

Diagnosis. Low- to moderately high-spired and turbiniform shell shape. The upper whorl surface forming an angle of <45 Ǫ with the selenizone located on the upper edge of whorl face. Sutures sharply defined. Upper whorl face with both spiral and collabral ornament; most strongly developed near the suture, weakest near the selenizone. Anomphalus to widely phaneromphalus, with or without funicle.

Remarks. These specimens resemble the Permian genera Wannerispira , Ananias and Glabrocingulum , and the Triassic genus Kamupena . They differ from Wannerispira by possessing a selenizone in the upper third of the whorl, and only having two rather than three strong spiral ribs; from Ananias by being low- rather than high-spired and having a less conspicuous and thinner concave band below the selenizone; and from Kamupena by lacking a strong umbilical callus plug. These specimens also differ from other neilsoniines by having spiral ribs and no axial ornamentation, and by being less elongated. Another genus with a comparable whorl profile is Rhaphistomella , which has been considered a synonym of Glabrocingulum ( Batten 1989; Erwin & Pan 1996), but it differs from these specimens by the absence of a prominent medial concave band and a more strongly nodulose keel under the suture. These specimens are therefore assigned to the genus Glabrocingulum .

Wannerispira is the only other unequivocal eotomariid genus to have been reported from the Early Triassic ( Kaim et al. 2010; Hautmann et al. 2015), and belongs to the Subfamily Neilsoniinae . Since Glabrocingulum , in contrast, is dextral, low- rather than high-spired, and with a moderately deep slit developing into a selenizone with rounded margins, it belongs within the Subfamily Eotomariinae . These specimens represent the first Early Triassic record of the Subfamily Eotomariinae and are the first Early Triassic record of the genus Glabrocingulum , which is rarely recorded after the Permian period.