Epidiceras carinatum

Epidiceras carinatum (Gemmellaro, 1875) Figs 4, 5, 6, 7, 8 v * 1875 Diceras carinatum, Gemm. – Gemmellaro: 28, pl. 5, figs 9, 10. v 1876 Diceras carinatum, Gemm. – Gemmellaro: 50, pl. 7, figs 9, 10. v 1881 Diceras bavaricum Zitt. – Boehm: 156 [82], pl. 25 [9], fig. 4, pl. 26 [10], figs 1–4, pl. 27 [11], figs 3, 4. 1976 Eodiceras bavaricum (Zittel) – Yamani: 6. 1999 Epidiceras bavaricum (Boehm, 1882) – Skelton: 84, pl. 1, figs 3–6. 2017 Epidiceras carinatum (Gemmellaro, 1876) – Schneider et al.: 58, pl. 22, figs A, B. Diagnosis. Large Epidiceras with up to 90 mm high, D-shaped commissure, the anterior margin forming the straight line of the D. Shell outside with a sharp carina extending from umbo to anterior-ventral corner, dividing the exterior of the shell into flattened anterior and posterior portions. Posterior myophore prominent and wide; anterior myophore less wide but distinct. Material. The type series of Diceras carinatum Gemmellaro, 1875 (late Tithonian; Palermo region, Sicily, Italy) consists of two originally figured specimens: a right valve (Gemmellaro 1875, pl. 5, fig. 9; accession number MGUP- 20-407.1), designated lectotype herein, and a left valve (Gemmellaro 1875, pl. 5, fig. 10; MGUP- 20-407.2), thereby becoming the only paralectotype. Note that Gemmellaro’s (1876) three-volume book, which is often cited as the original source of his species descriptions, is a collection of (parts of) 13 previously published journal articles by Gemmellaro and Gemmellaro and Di Blasi, which were reprinted with updated synonymies, modified or omitted introductions and in different order. Based on in-text citations and synonymies, the dates given (1868, 1869, 1871) are clearly erroneous, and the entire book was likely published in 1876, the date of the introduction. The original descriptions of the new rudist taxa from the ‘ Calcare a Terebratula janitor ’ are contained in the journal article by Gemmellaro (1875). The type series of Diceras bavaricum Boehm, 1881 (late Kimmeridgian; Kelheim Member, Frankenalb Formation; Kelheim area, Bavaria, Germany) originally consisted of 20 specimens (Boehm 1881: 157). Four specimens were figured, and three of these are preserved: a right valve (Boehm 1881, pl. 26, fig. 4; BSPG 1872 XI 556), designated lectotype herein; a left valve (Boehm 1881, pl. 26, fig. 3; BSPG 1872 XI 557), designated paralectotype 1; and an internal mould of a specimen with closed valves (Boehm 1881, pl. 27, figs 3, 4; BSPG 1872 XI 558), designated paralectotype 2. The fourth figured specimen, an individual with closed valves (Boehm 1881, pl. 25, fig. 4, pl. 26, figs 1, 2), as well as the remaining 16 non-figured specimens are lost. Numerous specimens are available from Saal, of which a representative suite was selected for measurements and / or figures for this study: a single slightly fragmentary juvenile right valve (BSPG 2016 XXI 1394); six double-valved specimens (BSPG 2016 XXI 69, BSPG 2016 XXI 1401, BSPG 2016 XXI 1402, BSPG 2020 CIII 30, BSPG 2020 CIII 31, BSPG 2020 CIII 32); thirteen left valves (BSPG 2016 XXI 13, BSPG 2016 XXI 1214 –1218, BSPG 2016 XXI 1222, BSPG 2016 XXI 1223, BSPG 2016 XXI 1225, BSPG 2016 XXI 1403, BSPG 2016 XXI 1523, BSPG 2020 CIII 6, BSPG 2020 CIII 26); and twenty right valves (BSPG 2016 XXI 67, BSPG 2016 XXI 68, BSPG 2016 XXI 1200 –1213; BSPG 2016 XXI 1219 –1221, BSPG 2016 XXI 1522). In addition, fragmentary internal moulds of two right valves (BSPG 2019 IV 1, BSPG 2019 IV 11) and one left valve (BSPG 2019 IV 12) are available. Measurements and figure numbers. Type locality and stratum. According to Gemmellaro (1875), the type material of Diceras carinatum was collected ‘ in the district of Fovara near Villabate, near Carini, in the surroundings of Torretta and in the district of Santa Maria di Gesù near Palermo’ [translated from Italian]. The museum catalogue lists three locality names, Carini, Favara and Favarotta, for the two originals archived under accession numbers MGUP- 20-407.1 and MGUP- 20-407.2. Consequently, the type locality cannot be established. Tithonian shallow marine limestones in the Palermo region occur within two different structural units, and the mentioned localities relate to both. Tithonian strata near Carini and Torretta conform to the informal Calcari di Piano Battaglia within the platform succession of the Panormide Unit (Catalano 2011 b; Catalano et al. 2013 b). In contrast, Tithonian strata near Villabate and Santa Maria di Gesù expose the informal Ellipsactinia breccias member of the Crisanti Formation, forming part of the basinal Imerese Unit (Catalano 2011 a; Catalano et al. 2013 a). Description. Large Epidiceras, with commissure typically between 70 and 90 mm high when adult. Sub-equivalve to moderately inequivalve, with rather gradually and slowly expanding whorls. Commissure D-shaped in outline, with anterior margin forming the straight line of the D; dorsal, posterior and ventral shell margins evenly rounded. Both valves strongly carinate, with carina extending from umbo to anterior-ventral corner, dividing exterior of shell into flattened anterior and posterior portions, the anterior one often being slightly larger. Right valve generally rather regularly coiled, auriculate in outline and shape in early growth (Fig. 7 A – C, 8 A – D). Left valve often more openly coiled and stretched, the largest, slightly fragmentary specimen from Saal surpassing 200 mm in height (Fig. 6 E). Ornament of radial costellae (spiral ornament, if one would apply gastropod terminology) preserved anterior to the carina in two large left valves, one of which is figured here (Fig. 8 G). Hinge plate of left valve high, with a single, strong, arcuate cardinal tooth 2 in sub-horizontal position, extending from near the anterior shell margin approximately halfway back. Cardinal tooth flanked by a shorter, moderately deep, sloping socket 3 a’ ventrally within the arch, and an extensive, very deep socket 3 b’ dorsally and posteriorly. Hinge plate of right valve equally high, dominated by very large, arcuate posterior cardinal tooth 3 b paralleling the dorsal shell margin; initially forming a raised arch, but becoming increasingly tongue-shaped and pointed, and bending upward in adulthood. Small peg-like anterior cardinal tooth 3 a situated ventrally, above a pronounced buttress, separated from 3 b by a deep, arcuate socket 2 ’. Nymphs not very prominent but distinct and long. Anterior myophore in both valves sharp and distinct, but forming a relatively low elevation below the hinge plate. Posterior myophore prominent and wide in both valves. Both myophores extending ventrally far below the hinge plate, providing space for large adductor muscles. Remarks. Before conducting the description of his new species, Gemmellaro (1875: 29) had received two right valves of ‘ Diceras ’ from the Kelheim area, sent from Munich by Karl Alfred von Zittel. These specimens are still part of the collections of the museum in Palermo. Based on comparison with his own material from Sicily, Gemmellaro (1875) considered the Sicilian and Bavarian specimens as conspecific and assigned them to his newly established species, Diceras carinatum. He further mentioned that Diceras carinatum, Diceras speciosum and Diceras muensteri were found in the same deposits at Kelheim. Boehm (1881) did not agree with Gemmellaro’s (1875) attribution of the Bavarian specimens and instead assigned them to Diceras bavaricum. He credited Zittel with the authorship of D. bavaricum, who had previously used this name on collection labels (Boehm 1881: 82). However, the name was not published and thus not available before Boehm’s (1881) monograph, and Diceras carinatum clearly takes priority, if considered conspecific. Boehm (1881) distinguished D. bavaricum and D. carinatum based on differences in the dentition of the right valve (which were not further explained), but also stated that the hinges of the 20 specimens of D. bavaricum at his disposal were highly variable. He further claimed that D. carinatum was almost equivalve, while D. bavaricum was strongly inequivalve. Both statements, however, are misleading. In the right valve figured by Gemmellaro, designated as the lectotype herein, the upper part of the large posterior cardinal tooth is broken – which accounts for the main ‘ difference’ in dentition compared to Diceras bavaricum of Boehm (1881). Secondly, Gemmellaro’s (1875) figured type material consists of one left valve and one right valve, which admittedly are of approximately the same size, but are not part of the same individual; their hinges do not match (Fig. 4). Consequently, it is impossible to assess to which degree the specimens from Sicily are equivalve. Furthermore, both specimens with closed valves figured by Boehm (1881, pl. 25, fig. 4, pl. 26, figs 1, 2 and pl. 27, figs 3, 4) are only slightly to moderately inequivalve. Moreover, the size and degree of uncoiling of the attached left valve of all epidiceratids varies greatly, depending on the substrate and immediate surroundings of an individual. Upon comparison of the type material of both Diceras carinatum and D. bavaricum, we revert to Gemmellaro’s (1876) opinion and consider D. bavaricum a junior subjective synonym of D. carinatum. The three specimens from Plagne, Département Ain, France, assigned to Epidiceras bavaricum by Skelton (1999: pl. 1, figs 4–6), also belong to Epidiceras carinatum (Gemmellaro, 1875). Epidiceras acutum (Boehm, 1883) from Štramberk in Czech Republic is the only species of Epidiceras that has a similarly carinate shell, but the carina is sharper; as a result, the anterior and posterior parts of each valve meet at a lower angle than in E. carinatum. Moreover, the anterior shell margin seems less straight, and the commissure thus less clearly D-shaped than in the latter. Given that Boehm (1883) only figured a single specimen with closed valves (which unfortunately has been lost), both the morphologic variability and inte