Leucosyrinx thisbe, comb. nov.

Leucosyrinx thisbe (E.A. Smith, 1906) comb. nov. Fig. 17A–E Pleurotoma (Surcula) thisbe E.A. Smith, 1906: 162. Pleurotoma (Surcula) thisbe – Annandale & Stewart 1909: pt. 6, pl. 20 figs 1–2. Comitas thisbe – Powell 1969: 276 (23–288), pl. 225 figs 1–2. non Comitas melvilli (Schepman, 1913) – Tan & Islami 2021: 326, fig. 9e. Type material Holotype SRI LANKA • SL 44 mm; off E of Ceylon; depth 1086 ftm (= 1986 m); ZSI, M 1233/1. Material examined (sequenced) SOLOMON ISLANDS • 1 lv; Savo; 9°4′ N, 159°38′ E; depth 1230–1306 m; SALOMONBOA 3, stn CP2781; MNHN-IM-2009-16821. Description SHELL. Large, reaching 75 mm. broadly fusiform, with high spire, from greyish to light brownish, thick and solid. Protoconch unknown. Teleoconch whorls distinctly roundly angular on shoulder, subsutural ramp significantly deepened in relation to shoulder, concave or with nearly flat side. Medium pronounced to strong subsutural cord. Channeled suture. 18–19 strong, oblique, sinuous axial folds on and below shoulder on last and penultimate whorls, reaching lower suture on upper whorls and extend to shell base on last whorl. Well-developed spiral sculpture of similar in width, rather broad, low, rounded, and wavy cords over entire shell, including subsutural ramp, with intervals narrower than cords’ width. Shell base medium convex, rapidly passing into medium-long straight canal. Rather broad, elongate-oval aperture, well differentiated from canal. Well-developed white columellar and parietal callus. Deep, subsutural, broadly arcuate anal sinus extends across subsutural ramp, confluent with large forward extension of outer lip. RADULA (studied in MNHN-IM-2009-16821). Typical of genus, duplex marginal teeth ~570 µm in length (2.8% AL without canal). DNA diagnosis (based on 1 (!) cox 1 sequence) ‘A’ in site 88, ‘G’ in site 196, ‘G’ in site 544. Remarks This very distinct and very large species (SL up to 75.1 mm) is represented in our material by a single specimen. Contrary to most studied species of Leucosyrinx, L. thisbe comb. nov. has a strong thickened subsutural cord (more prominent in our specimen than in the holotype), and correspondingly, the suture is broadly channeled, while the subsutural ramp is significantly deepened in relation to the shoulder. Another unusual character is that very distinct sinuous axial folds (19 on the last whorl and similar number according to the photo of the holotype) extend well to the shell base and reach to the lower suture on the teleoconch whorls. The species was known before from a single worn holotype with missing apex and strongly eroded upper whorls. We attribute our specimen to the species with some reservation. Our specimen is much larger (75 mm vs 44 in holotype), and the last whorl is more gradually constricting passing in the canal in comparison with the holotype. Both our specimen and the holotype were collected at large depths 1230–1306 and 1986 m, respectively. Tan & Islami (2021: fig. 9e) illustrated an additional specimen as Comitas melvilli. Their specimen is very similar to the holotype, although having a better pronounced subsutural cord, like in our specimen. Leucosyrinx melvilli (Fig. 17I–J), known only from the holotype, lacks the subsutural cord and has weaker and more numerous axial folds. There is some similarity of L. thisbe comb. nov. to L. eurina in spiral and axial scultpture, as well as in the presence of a subsutural cord. Nevertheless, L. thisbe differs in having a higher last whorl, more gradually constricting while passing into canal. Distribution From Sri Lanka to Solomon Is., 1230–1986 m.