Reclassification of gastropod Proscutum Fischer based on muscle scars and shell structure

Shells of the Recent emarginuline fissurellid Scutus Montfort have a horseshoe-shaped, anteriorly open muscle scar and a posterior apex. Small Scutus-like shells from the Paris Basin [France] Eocene, reported to have an anteriorly open scar, have been referred to Proscutum Fischer, which was considered a subgenus of Scutus. Examination of 9 species referred to Proscutum, including the type, P. compressum (Deshayes), shows that the scar has been erroneously described and illustrated as open anteriorly. Consequently the anterior-posterior orientation of the shell has been misinterpreted. Actually the muscle scar is typical patellacean and the antero-posterior axis is reversed from the previously accepted orientation. Additionally, a radial crossed-lamellar shell layer (not present in the Fissurellidae) is present in Proscutum just dorsal to the myostracum (muscles scar shell layer). Because of these characters Proscutum is transferred from the family Fissurellidae of the suborder Pleurotomariina to the superfamily Patellacea of the suborder Patellina. In Proscutum the 2 shell layers just dorsal to the myostracum are, respectively, radial cross-lamellar and concentric cross-lamellar. Within the Patellacea this shell layer sequence is present only in the patellid subfamily Patellinae. Accordingly, Proscutum is assigned to that subfamily.

This record provided courtesy of AGI/GeoRef.