Morphology of the carapace and of the chela of the first pair of pereiopods of Palaeastacus Bell, 1850 and species from the Early Jurassic. A: typical carapace groove pattern of Palaeastacus; B: typical chela of the first pair of pereiopods of Palaeastacus; C–E: holotype MSNM i7606 of Palaeastacus meyeri (Garassino, 1996) from the Sinemurian of Osteno (Italy): counterpart (C), general view (D), line drawing of the carapace and P1 chelae (E); F: original figure of Oppel (1862: pl. 4, fig. 5) of the holotype of Palaeastacus numismalis (Oppel, 1853) n. comb. from the Pliensbachian of Gomaringen- Hinterweiler (Germany); G–I: specimen of P. numismalis n. comb. from the Pliensbachian of Böbingen an der Rems (Germany) in Thomas Balle’s collection, Alfdorf: lateral view (B), anterior view (C), schema of the carapace (D). Scale bars: 1 cm. Abbreviations: a: branchiocardiac groove; as: antennal spine; b: antennal groove; b₁: hepatic groove; c: postcervical groove; d: gastro-orbital groove; e₁e: cervical groove; i: inferior groove; ip: intercalated plate; PoA: postorbital area; os: orbital spine; χ: attachment site of adductor testis muscle; ω: attachement site of mandibular muscle. Photographs: A. Garassino (C–D), W. K. Mayer (G, I). Line drawings: J. Devillez.