Costinuculana magharensis n. gen. n. sp. (Bivalvia, Nuculanidae) from the Middle Jurassic of Gebel Maghara, North Sinai, Egypt Wagih S. Ayoub-Hannaa, 1,2 Ahmad A. Abdelhady, 3 and Franz T. Fürsich 2 1 Geology Department, Faculty of Science, Minufiya University, El-Minufiya, Shibin El Kom, Egypt 〈wagih_hannaa@yahoo.com〉 2 FG Paläoumwelt, Geozentrum Nordbayern der Friedrich-Alexander Universität Erlangen-Nürnberg, Loewenichstrasse 28, D-91054 Erlangen, Germany 〈franz.fuersich@fau.de〉 3 Geology Department, Faculty of Science, Minia University, 61519 Minia, Egypt 〈alhady2003@yahoo.com〉 Abstract.—The nuculanid bivalve Costinuculana magharensis new genus new species is described from the middle to upper Bathonian Kehailia Formation of Gebel Maghara, North Sinai, Egypt. Costinuculana differs from other genera of the family Nuculanidae by the presence of opisthocline ribs along the rostrum. These ribs are variable in shape and size, straight to folded posteriorly, bifurcate ventrally and occasionally postero-dorsally, and cover an area ~45% of the total valve length from the posterior end. The life position of C. magharensis n. gen. n. sp. is reconstructed on the basis of a functional interpretation of its morphology and by comparison with closely related Recent forms. The asymmetrical commarginal ribs facilitated the burrowing process. The posterior oblique ribs are asymmetrical in cross-section with a steeply concave side in the burrowing direction and slightly convex side in the opposite direction. They probably kept the bivalve in a stable position once the desired depth had been reached. The thick oblique ribs probably also increased the strength of the rostrum and offered resistance against durophagous predators, being presumably partly exposed above the sediment-water interface. Based on the associated fauna, Costinuculana n. gen. lived in a low-energy environment characterized by a fine-grained, soft substrate. Introduction Gebel Maghara is a dome-like structure covering ~400 km 2 in the northern Sinai, 50 km south of the Mediterranean coast (Fig. 1). It comprises the thickest and most complete Jurassic outcrop in northern Sinai (1800 m; Al Far, 1966; Keeley, 1994). The Middle–Upper Jurassic succession of Gebel Maghara is well known for its rich and diverse macrobenthic fauna such as brachiopods, bivalves, gastropods, ammonites, and corals. This fauna has been repeatedly studied from a taxonomic point of view (e.g., brachiopods: Farag, 1957, 1959; Farag and Gatinaud, 1960a, b; Feldman, 1987; Hegab, 1989, 1991; Feldman et al., 1991, 2012; bivalves and gastropods: Douvillé, 1916, 1925; Hirsch, 1980; and ammonites: Arkell et al., 1952; Parnes, 1988). The most-recent studies dealing with the strati- graphy and paleoecology are given by Abdelhady (2014) and Abdelhady and Fürsich (2014, 2015a, b, c). The purpose of this paper is: (1) to describe the new bivalve taxon Costinuculana magharensis n. gen. n. sp. (order Nuculanida) from the Bathonian of Gebel Maghara and to compare it with similar taxa of the family Nuculidae; (2) to interpret the function of its oblique ribs, which cover an area up to ~45% of total valve length from the posterior end and to reconstruct its autecology; and (3) to determine its paleo- environmental setting on the basis of facies relationships and associated faunal elements. Geologic setting The Jurassic succession of Gebel Maghara represents a sequential development of continental and marine sediments, starting in the Early Jurassic (Toarcian) and lasting until the Kimmeridgian (Fig. 2). It represents a wide variety of continental, deltaic, nearshore-siliciclastic, and carbonate-shelf environments (Al Far, 1966; Picard and Hirsch, 1987), and contains a rich macrofauna. The marine strata are represented by the Rajabiah, Bir Maghara, and Masajid formations, whereas the continental sediments include the Mashabba, Shusha, and Safa formations. The nuculanid specimens have been collected from the middle to upper Bathonian Kehailia Formation (Fig. 2). This formation represents the lower member of Al Far’s (1966) Masajid Forma- tion (Kehailia Member). The Kehailia Formation unconformably overlies the lower Bathonian Safa Formation and underlies the Callovian Arousiah Formation (Fig. 2). It consists of yellow, highly fossiliferous marly silts and marls with thin, yellow glauconitic limestone intercalations and occasional sandstone interbeds. For more details about litho- and biostratigraphy see Abdelhady (2014) and Abdelhady and Fürsich (2015a, b, c). Materials and methods The present study is based on 10 specimens with preserved shells that were collected from the middle to upper Bathonian Journal of Paleontology, page 1 of 10 Copyright © 2017, The Paleontological Society 0022-3360/15/0088-0906 doi: 10.1017/jpa.2016.161 1 https://doi.org/10.1017/jpa.2016.161 Downloaded from https:/www.cambridge.org/core. IP address: 93.91.80.7, on 12 Feb 2017 at 11:28:21, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms.