Flexopteron liancurtense Merle, Pacaud, Ledon & Goret, 2024, n. sp.

Flexopteron liancurtense n. sp. (Figs 20 E-H; 28A, B) urn:lsid:zoobank.org:act: 6CA77DFC-A09D-4A63-A2B4-55305DD23 BEC Murex (Poirieria) foliaceus – Cossmann & Pissarro 1911: pl. 36, fig. 169-17 [non Melleville, 1843]. Poirieria (Flexopteron) foliacea – Le Renard & Pacaud 1995: 114, Ref. GA169-17 [non Melleville, 1843]. Vauxyrytis liancurtensis – Merle 1999: 459, pl. 68 (unpublished thesis) (nomen nudum). TYPE MATERIAL. — Holotype. France • Paris Basin, Oise, Liancourt-Saint-Pierre; Sables d’Hérouval (biozone NP12); early Eocene (Ypresian); MNHN.F.J02578 (Cossmann coll.), figured specimen in Cossmann & Pissarro (1911: pl. 39, fig. 169-17), H: 7.7 mm (Figs 20E, F; 28A). Paratypes. France • 1 spm; same as for the holotype; MNHN.F.A77758 (Merle coll.) (Figs 20G, H; 28B) • 17 spm; idem; MNHN.F.A77759 (Merle coll.) • 9 spm; idem; MNHN.F.J17633 (Cossmann coll.); • 1 spm; Paris Basin, Oise, Hérouval; Sables d’Hérouval (biozone NP12); early Eocene (Ypresian); MNHN.F.B63662 (Morlet coll.) • 29 spm; idem; MNHN.F.A90913 (Pacaud coll.). ETYMOLOGY. — From the Latin adjective liancurtense in reference to the type locality, Liancourt-Saint-Pierre (Oise). TYPE HORIZON. — Sables d’Hérouval (biozone NP12), see Gély & Lorenz (1991: pl. 1), early Eocene (Ypresian). TYPE LOCALITY. — France, Paris Basin, Oise, Liancourt-Saint-Pierre, see Fritel (1910: 190). DISTRIBUTION. — Paris Basin (France), early Eocene (Ypresian, Hérouval Formation only). DESCRIPTION Smooth, conical multispiral protoconch of around three whorls. Sinusigeral scar well marked. Biconic teleoconch up to 7 mm in height, up to 4 mm in width (including cord spines). Moderately high spire, up to four subcarinate whorls. Last whorl (fourth whorl) up to 68% of total length. Apical angle 54° including P1 spine. Spiral sculpture with marked primary cords. First whorl: no cord; second whorl: appearance of P2 weak; third whorl: development of P1 spine and appearance of P3 above suture line. Fourth and last whorl: no primary cord on sutural ramp, P1 to P5, s1 and s2 moderately marked, P6 and ADP weak on siphonal canal. Axial sculpture with 11 lamellose varices on first whorl, 13 on second, and 14 on third and fourth. Varices axially aligned in a zig-zag fashion. Ovate aperture up to 36% of diameter and up to 77% of length of the last whorl (including siphonal canal). Columellar lip slightly erect anteriorly, adherent posteriorly, usually smooth or occasionnally with one tubercle. No anal sulcus, no parietal callus. Outer lip with small denticles. D1 to D5 simple, D1 more developed than other denticles. Outer lip not crenulate. Shoulder sinus of P1 spine widely open, shallow. Pseudoumbilicus narrow. Siphonal canal open, up to 36% of the apertural length and slightly dorsally recurved. COMPARISONS Melleville (1843) described Murex foliaceous for a small Ypresian Flexopteron displaying axially zizgaging lamellae and a short P1 spine. Later, Cossmann (1889) described Murex dyscritus which bears less marked primary cords than Murex foliaceous. However, numerous specimens housed in the MNHN show many transitional forms suggesting these differences represent intraspecific variation. Thus, the older binome Murex foliaceous takes nomenclatural priority. Moreover, Cossmann & Pissarro (1911) illustrated an atypic specimen from the Ypresian of Liancourt-Saint-Pierre (Hérouval Formation), squatter than usual for F. foliaceum, with a bent siphonal canal, poorly developed P1 spines, more marked primary cords and occasionally a tubercle on the columellar lip. This specimen from Liancourt is not a pathological specimen and all specimens from this locality and Hérouval display similar morphology. They differ from F. foliaceum (also found at Liancourt-Saint-Pierre) by having spiral cords P1 and P2 appearing earlier in ontogeny. Merle (1999, unpublished thesis) illustrated several other specimens and the ontogenetic changes in their spiral sculpture. He considered this population as a different species and named it Vauxyrytis liancurtensis. However, Merle (1999) is an unpublished thesis and the name is a nomen nudum made available herein. Placement of this species in the genus Vauxyrytis Merle, 1999 (nomen nudum), an unpublished genus corresponding to Beyregrex Merle, n. gen. (see below), was based on the shape of the varices, which are not spiny, and the occasional presence of a columellar tubercle. Nevertheless, we found some specimens of F. liancurtense n. sp. with P1 spines and several species of Flexopteron can have a columellar tubercle [e.g., F. ogormani (Cossmann, 1923)]. In addition, F. liancurtense n. sp. clearly resembles a Tortonian species from NW France: F. gallicum (Landau, Merle, Ceulemans & Van Dingenen, 2019), see Landau et al. (2019: pl. 11). Thus, we attribute this species to Flexopteron.