Lutonautilus cratus Korn & Hairapetian, 2025, gen. et sp. nov.

Lutonautilus cratus gen. et sp. nov. urn:lsid:zoobank.org:act: FA260A86-6965-469D-96FE-D7D6B45B5F8A Fig. 20; Table 14 New genus, new species – Korn 2025: 58, fig. 29. Diagnosis Species of Lutonautilus gen. nov. with thinly discoidal, subinvolute conch (ww/dm =0.35–0.40; uw/ dm= 0.35–0.40), nearly equidimensional whorl profile (ww/wh= 0.95–1.05) and high to very high coiling rate (WER =2.20–2.35) at a conch diameter of 60–80 mm. Whorl profile with gently convergent flanks; venter broadly rounded, flanks slightly flattened, umbilical margin rounded, umbilical wall flattened. Sculpture with about 25 blunt lateral ribs per volution; they begin on the outer umbilical wall and are strengthened on the ventrolateral shoulder to form elongate nodes. Suture line with a shallow external lobe and a shallow, broadly rounded lateral lobe. Etymology From the Greek ‘κρατύς’=‘strong’; because of the rather robust conch and sculpture. Type material Holotype IRAN – Esfahan Province • Baghuk Mountain; Hambast Formation, Vedioceras beds (late Wuchiapingian); 2011; Korn et al. leg.; illustrated in Fig. 20A–D; MB.C.32126. Paratypes IRAN – Esfahan Province • 1 specimen; same data as for holotype; 2010; Korn et al. leg.; illustrated in Fig. 20E–F; MB.C.32127 • 2 specimens; same data as for holotype; 2010; Korn et al. leg.; MB.C.32128, MB.C.32129. Description Holotype MB.C.32126 is a rather complete, but somewhat corroded specimen with a conch diameter of 88 mm (Fig. 20A, D). It is almost completely chambered and only a little more than a quarter of the last whorl belongs to the body chamber. The conch is thinly discoidal and subevolute (ww/dm =0.33; uw/dm= 0.38) with a high coiling rate (WER =2.17). The whorl profile is almost square-shaped (ww/ wh= 0.95) and shows a flatly rounded venter and a broadly rounded ventrolateral shoulder. The flanks are slightly flattened and slowly convergent; the umbilical margin is continuously rounded and the umbilical wall is steep (Fig. 20B). The sculpture consists of about 25 blunt ribs on the flank; the ribs and their interspaces have almost the same width. These ribs already begin in the outer area of the umbilical wall and from there, they follow a weakly backwardly directed course; they extend across the flank with a broad and shallow sinus and are strengthened to form radially elongated nodes in the area of the ventrolateral shoulder. There they suddenly weaken and diminish; no ribs are visible on the venter. The suture line shows a very shallow external lobe and a broadly rounded lateral lobe (Fig. 20C). The last half whorl of the phragmocone has about 12 chambers (CLI=15). Paratype MB.C.32127 is a fragment of a specimen with a conch diameter of 76 mm (Fig. 20F). The conch geometry is largely the same as in the holotype, but the paratype has a slightly more compressed whorl profile (ww/wh = 0.93) and a higher coiling rate (WER =2.35). The sculpture is better preserved than in the holotype; it shows 16 rather sharp ribs on the last half volution; these ribs start on the umbilical wall and thin out at the ventrolateral shoulder. The ribs are somewhat narrower than their interspaces; they extend across the flank with a shallow sinus. Remarks Lutonautilus cratus gen. et sp. nov. differs from the co-occurring L. elachus gen. et sp. nov. in the slenderer whorl profile (ww/wh= 0.95–1.05 in L. cratus but ~ 1.15 in L. elachus), the stronger convergent flanks (nearly parallel in L. elachus) and the wider umbilicus (uw/dm = 0.35–0.40 in L. cratus, but only ~ 0.30 in L. elachus). Furthermore, the ribs begin in the outer area of the umbilical wall in L. cratus, but at the umbilical margin in L. elachus. Lutonautilus cratus gen. et sp. nov. differs from L. cymus gen. et sp. nov. in the shape of the ribs, which in L. cratus are almost straight on the flanks, while they extend with a concave arch in L. cymus. The ribs of L. cratus are coarse in the midflank area, while they are weakly developed in the middle of the flank in L. cymus and strengthened and forming nodes on the outer and inner flanks.