Revision of Syncyclonema (Upper Cretaceous) and comparison with other small pectinid bivalves and Entolium
New descriptions and figures are given for Pecten rigida Hall & Meek ( = Pecten halli Gabb), the type species of Syncyclonema Meek, and for the type species of genera to which Syncyclonema is often compared: Entolium Meek, Eburneopecten Conrad, Pectinella Verrill, Hyalopecten Verrill, Camptonectes Agassiz, Micronectes Ichikawa & Maeda, Pseudamussium Mörch, and "Pseudamussium" H. & A. Adams. Syncyclonema is shown to be a valid genus. A lectotype is designated for Syncyclonema halli, and on the basis of its chlamyiid shape, deep byssal notch, and hinge morphology Syncyclonema is placed in the family Pectinidae. These characters invalidate synonymy of Syncyclonema with Entolium and its assignment to the family Entoliidae Korobkov.