Order Pleurotomariida Cox & Knight 1960
Superfamily Eotomarioidea Wenz, 1938
Family Gosseletinidae Wenz 1938
Genus Glabrocingulum Thomas 1940

Since the early 1800s, several authors (Norwood & Pratten 1855, others) have placed species of fossil gastropods under what became a catch-all genus, Pleurotomaria Defrance 1826. If a gastropod had a selenizone (a slit shell), it probably ended up in the genus. While authors divided and assigned several to new or different genera, Glabrocingulum was one of the last to receive reassignment. Thomas (1940) named Glabrocingulum during her review of the Scottish Carboniferous Pleurotomariidae.

Wenz named the Eotomariidae for shells with a slit appearing on the outside of the aperture with a concave selenizone, usually at mid-whorl. Today, the name is used for a superfamily, family, and subfamily. Gordon and Yochelson (1987) named the tribe Glabrocingulides, noting its “anamphalous to minutely phaneromphalus” umbilicus and “projecting flanges” on either side of the selenizone among other features that together are diagnostic for Glabrocingulum. The genus is also common; the pair said that Glabrocingulum is the single most abundant Pennsylvanian gastropod genus in North America.

Glabrocingulum are uncommon but easy to identify from either Armstrong County locality. The pleural angle ranges from 96–112 degrees, according to Karapunar et al. (2022). The genus is often misidentified; the authors spent five paragraphs making and explaining corrections to previous errors in the literature. The spire and base share the same shape, with a rounded base. The selenizone with the bordering flanges has prosocline ornament in the upper whorls and opisthocline lines immediately below the selenizone flange. The specimens tend to be smaller and are not always preserved with great detail.

Glabrocingulum sp. from the Pine Creek limestone at SL 6445.
Fig. 1.—Glabrocingulum sp. from the Pine Creek limestone at SL 6445. A–B, a specimen in two views, showing the ornament and selenizone, CG-0545; C, aperture view of a specimen showing the outline of the aperture with selenizone profile, CG-0554; D, a specimen with a rounder whorl profile, CG-0544. Scale bar = 5 mm.
Glabrocingulum sp. from the Pine Creek limestone at SL 6445
Fig. 2.—Glabrocingulum sp. from the Pine Creek limestone at SL 6445. A, apertural view of a specimen with a well-preserved column, CG-0553; B, abapertural view showing a distinct selenizone and raised ornament nodes at upper whorl, CG-0539; C, uncleaned specimen in apertural view showing the distinct whorl profile, CG-0541. Scale bar = 5 mm.
Glabrocingulum sp. from the Pine Creek limestone at SL 6445.
Fig. 3.—Glabrocingulum sp. from the Pine Creek limestone at SL 6445. A–C, a specimen in three views. A, apertural view; B, spire view; C, basal view, CG-0461; D, specimen in apertural view showing shell ornament and selenizone, CG-0394. Scale bar = 5 mm.

References

Late Carboniferous Fossils from the Glenshaw Formation in Armstrong County, Pennsylvania

Localities: Locality SL 6445 | Locality SL 6533

Trilobita | Crinoidea

Bivalvia: Allopinna | Parallelodon | Septimyalina

Cephalopoda: Metacoceras | Poterioceras | Pseudorthoceras | Solenochilus

Gastropoda: Amphiscapha | Bellerophon | Cymatospira | Euphemites | Glabrocingulum | Meekospira | Orthonychia | Patellilabia | Pharkidonotus | Retispira | Shansiella | Strobeus | Trepospira | Worthenia

Brachiopoda: Cancrinella | Composita | Isogramma | Linoproductus | Neospirifer | Parajuresania | Pulchratia

Chordata: Petalodus | Glikmanius