Palaeoentolium Romanov, 1985
ROMANOV, L. F. 1985. Jurassic pectinoids from southern USSR. Kishinev. Shtiintsa. 231 p., pls. 1-30 (in Russian).
Entolium discites (Schlotheim); A. Allasinaz, 1972, Revisione dei Pettinidi triassici, plate 35, figures 8, 9.
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«(a) The subfamily Palaeoentoliinae Romanov, 1985 is regarded as the paraphyletic stem group of the Entoliidae. As emended herein, members of this group have ontogenetically abbreviated prismatic calcite or none at all on the outer surface of the right valve. A nonprismatic calcitic outer layer on each valve is underlain by a thicker inner aragonitic crossed-lamellar layer. This inner layer is extensive, extending nearly to the disk and auricle margins and comprising the hinge structures, internal disk buttresses, and basal auricular buttresses. The shape is amusiiform, with auricles relatively small compared with the size of the disk and a byssal notch that becomes obsolete in mid- or late ontogeny. The shell exterior is in general remarkably smooth, with only commarginal lirae or lamellae present and radial costae or well-developed radial plicae absent. Microsculpture, if present, generally consists of very fine, shallow pits in an antimarginal or commarginal pattern.
This emended concept of the Palaeoentoliinae is based on shell microstructure and mineralogy, characters not considered by Romanov (1985), resulting in a reclassification of the five genera that Romanov (1985: 34) originally assigned to the subfamily: Palaeoentolium Romanov, 1985, Filopecten Allasinaz, 1972, Entolioides Allasinaz, 1972, Calvaentolium Romanov, 1985, and Neoentolium Romanov, 1985. Three of these, Filopecten, Entolioides, and Calvaentolium, are transferred in the present study to the family Entolioididae on the basis of their possession of an outer columnar prismatic layer on the right valve persisting throughout ontogeny. Neoentolium is an objective junior synonym of Cingentolium Yamani, 1983, regarded herein as a member of the subfamily Entoliinae and discussed below under that subfamily. The only genus remaining is therefore the type genus, Palaeoentolium, the interpretation of which depends on the morphology of Pleuronectites discites Schlotheim, 1820, designated the type species of the genus by Romanov. Unfortunately, there is a long history of problems and misunderstandings concerning this species that Romanov did not consider.» WALLER, T. R. 2006. Phylogeny of families in the Pectinoidea (Mollusca: Bivalvia): importance of the fossil record. Zoological Journal of the Linnean Society, 148: 313-342, figs. 1-12. [p. 324, 325]
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