Beloptera aff. longa Naef, 1922

Beloptera aff. longa Naef, 1922

Fig. 4d–k View Fig

Material: Three moderately preserved specimens ( IGS-DYM 01/06 to IGS-DYM 01/08) from the Priabonian Mandrykivka Beds of the Rybalsky Quarry, Dnipro.

Description: The specimen IGS-DYM01/06 ( Fig. 4d–f View Fig ) is a moderately preserved elongated (L 2 /W 2 = 2.51; see Table 2) guard-like sheath, which is slightly curved ventrally; it is 34.6-mm-long with semicircular in outline lateral expansions inclined towards the venter, which gives a convex form to the dorsal surface and a corresponding concavity to the venter. The lateral expansions are thick at the contact area of the rostrum and sheath and become gradually thinner to the periphery. The dorsal surface is roof-like with a raised narrow medial zone and steep slopes gradually turning into lateral expansions. The rostrum is nearly triangular in cross-section and gradually widens; its apex is rounded; the rostrum is slightly curved ventrally and the guard-like sheath is somewhat arched longitudinally. The ventral surface is covered with very small elongate pits at the base of the lateral expansions and very fine radial grooves on the rostrum. The dorsal surface is almost smooth with very fine radial grooves on the rostrum and front zones of the lateral expansions.

Specimen IGS-DYM01/07 ( Figs. 4 View Fig g-i) is a moderately preserved elongated (L2/W2 = 2.0) guard-like sheath that is slightly curved ventrally; it measures 21.4 mm long with lateral expansions that are inclined towards the ventral surface, which causes a convex shape towards the dorsal surface and a corresponding concavity towards the ventral surface. The lateral expansions are thick in the area of contact between the rostrum and the sheath and gradually thinning towards periphery. The dorsal surface is roof-like with a raised narrow medial zone and steep slopes gradually turning into the lateral expansions. The rostrum is nearly triangular in cross-section and gradually widens; its apex is rounded in the ventral aspect and slightly pointed in the lateral aspect; the rostrum is slightly curved ventrally and the guard-like sheath is somewhat arched longitudinally. The ventral surface is covered with very small elongate pits at the base of the lateral expansions and very fine radial grooves on the rostrum. Most of the dorsal surface is smooth; only shallow marks of blood vessels occur on the preserved lateral expansion and very fine radial grooves are on the rostrum.

The specimen IGS-DYM01/08 ( Fig. 4j, k View Fig ) is represented by a fragment of a rostrum that is nearly triangular in cross-section with a part of the lateral expansions. This poorly preserved fossil is indistinguishable from the specimen IGS-DYM01/06.

Remarks: The specimen IGS-DYM01/06 described above is better preserved than the single specimen of Beloptera cf. longa (IGS NASU-15/02) described in the work of Dernov & Demianov (2023: Fig. 6A–E). In particular, IGS-DYM01/06 shows that, unlike B. belemnoidea , the lateral expansions of B. aff. longa have semicircular margins, while in B. belemnoidea they are wavy (cf. Fig. 3a View Fig in this work). In contrast to B. cf. longa (IGS NASU-15/02), the specimen IGS-DYM01/06 is less ventrally curved and bears thin radial grooves on the anterior part of the dorsal surface of the lateral expansions.

The described specimens differ from the specimens of B. longa , figured by Edwards & Wood (1877: pl. 2, fig. 1), Naef (1922: figs 18a–g) and in Fig. 4a–c View Fig in this paper by a less massive rostrum. B. aff. longa differs from the most morphologically similar species B. belemnoidea in a very convex smooth dorsal surface, a greatly curved ventrally guard-like sheath and the nearly triangular in cross-section rostrum.

Occurrence: Bartonian of England, Priabonian of Ukraine.