Saalidiceras syllai Schneider & Werner, 2026, gen. et sp. nov.

Saalidiceras syllai gen. et sp. nov. Figs 9, 10 Diagnosis. As for genus. Etymology. In honour of the late Jürgen Sylla, amateur fossil collector from Sauerlach, Upper Bavaria, Germany, who collected the holotype and one of the paratypes. Material. Holotype, specimen with contiguous valves; BSPG 2016 XXI 1366. Paratype 1, specimen with contiguous valves; BSPG 2016 XXI 1368. Paratype 2, specimen with contiguous valves; BSPG 2022 X 5. Paratype 3, specimen with contiguous valves; BSPG 2022 X 6. Two fragments of left valves (not figured); BSPG 2016 XXI 1367, BSPG 2022 X 7. Poorly preserved right valve (not figured); BSPG 2016 XXI 369. Measurements and figure numbers. Type locality and stratum. Frankenalb Formation, Kelheim Member; late Kimmeridgian; Saal an der Donau, Lower Bavaria, Germany. Description. Shells moderately large for epidiceratids; total shell length of 63 mm and shell height of 85 mm in holotype; distinctly but moderately inequivalve. Commissure crescent in outline, 63 mm high in holotype, with two massive, very prominent, broadly rounded keels joining the endpoints of the crescent, enclosing a broad anterior trough with evenly rounded slopes. Coiling axes steeply inclined; directed downward-inward and slightly backward. Left valves of holotype and paratype 3 with approximately 1.75 whorls, resembling a corkscrew in shape. Attachment surface indistinct, very small in holotype; not preserved in paratypes. Right valve only with half a whorl or slightly more, forming a rapidly widening, incurved anterior trough. Shell interior, including hinge, unknown. Remarks. With its corkscrew-shaped left valve and the curved, trough-shaped right valve, Saalidiceras syllai is so entirely distinct from any other Jurassic rudists that it cannot be confused. The four double-valved specimens illustrated in Figs 9, 10 display a certain amount of variability with regard to the dimensions of the commissure relative to shell size, and also with regard to the elongation of the left valve. In paratype 3, the left valve is distinctly more openly coiled than in the other specimens; at the same time, its commissure is shorter and less high (Fig. 10 D). While the bizarre morphology of the species is well preserved in the type series, its hinge and musculature remain unknown, and all specimens are affected by diagenesis, where parts of the original shell are decayed to chalky matter that is barely distinguishable from the surrounding matrix, making preparation a difficult task. The calcitic outer shell layer, which we assume was present, is no longer preserved; as a result, it is unknown whether the shell surface was ornamented or not. Not having observed the specimens in situ, we can only speculate about their life style and potential functional aspects of their peculiar morphology. The indistinct or very small attachment surface seems unsuited to keep such large shells upright. Possibly, part of the left valve was submerged in soft sediment, anchoring the animal in the same way a manmade screw would do. Alternatively, adults may have been edgewise recliners sensu Seilacher (1984), resting either on their anterior side, in a similar fashion as suggested for Opisoma by Seilacher (1990) and Aberhan and Hillebrandt (1999), or on their posterior keels, as advocated for the same taxon by Posenato et al. (2013). Occurrence. Only known from the type locality.