Athleta (Volutocorbis) burtoni Vredenburg, 1923

Merle, Didier, Pacaud, Jean-Michel, Métais, Grégoire, Bartolini, Annachiara, Lashari, Rafiq A., Brohi, Imdad A., Solangi, Sarfraz H., Marivaux, Laurent & Welcomme, Jean-Loup, 2014, Volutidae (Mollusca: Gastropoda) of the Lakhra Formation (Earliest Eocene, Sindh, Pakistan): systematics, biostratigraphy and paleobiogeography, Zootaxa 3826 (1), pp. 101-138 : 121-122

Athleta (Volutocorbis) burtoni Vredenburg, 1923

( Fig. 9A–G )

Athleta (Volutocorbis) burtoni Vredenburg, 1923: 261 , pl. 15, fig. 2. Athleta (Volutocorbis) victoriae Vredenburg, 1923: 260 , pl. 15, figs 4. Athleta (Volutocorbis) burtoni . Cotter in Vredenburg 1928: 37. Volutocorbis soriensis Eames, 1952: 109 , pl. 4, fig. 95a–b.

Volutocorbis burtoni . Glibert 1960: 48 [new combination].

Description. Shell biconic, H 22, D 11 mm. Protoconch and two first teleoconch whorls unknown; at least 5 teleoconch whorls. Spire moderately high, occupying 21% of total shell height. Spiral whorls convex, last whorl rather oval. Spiral sculpture on spire of first row a subsutural nodules, becoming more developed apically; abapically, one or two rows of nodules including shoulder row, which is less distinct than other rows ( Fig. 9F ). On last whorl, spiral sculpture displaying: 1) subsutural row of nodules; 2) shoulder row of nodules; 3) abapically, 13–15 rows of almost rounded nodules, becoming less prominent on base. From second to last whorls, costae interrupted by rows of nodules. On last whorl, costae rather low, cut into prominent small, regular nodules by broad spiral grooves. Third whorl: 15–16 costae; fourth whorl: 14–19 costae; fifth and last whorl: 19–20 costae. Aperture ovate, rather narrow, occupying 75% of total height, 42% of diameter. Inner lip straight, columella with two folds, succeeded posteriorly by one or two weaker folds. Inner lip callus very narrow, not spreading. Outer lip thin, not thickened externally. Siphonal canal short; siphonal notch shallow.

Material. 1 spm (stn 1: CPAG.RAN. I.33, cast MNHN.F. A50371 ); 3 spm (stn 2: 1 spm CPAG.RAN. I.31, cast MNHN.F. A50369 ; 2 spm MNHN); 1 spm (stn 3: CPAG.RAN. I.32, cast MNHN.F.A50370); 3 spm (Jhirak, Lakhra Formation; Cossmann coll., MNHN.F. J12748 , MNHN.F. J13433 –34).

Comments. Athleta (Volutocorbis) burtoni was originally described by Vredenburg (1923) from the Lakhra Formation. Until now, it was recorded only from the Lakhra formation, but several specimens have been collected in marine sediments from the uppermost Bara Formation (see Geological setting). According to Vredenburg (1923), A. (V.) burtoni can be distinguished from A. (V.) eugeniae . Unfortunately, this author did not give diagnostic characters distinguishing the two species. He compared A. (V.) burtoni with a Bartonian species from the Paris Basin, A. (V.) digitalinus (Lamarck, 1811) [= Buccinum scabriculum sensu Solander in Brander, 1766 partim, non Linnaeus, 1758], because of its sculpture characterized by the presence of rounded nodules. A. (V.) burtoni differs obviously from A. (V.) eugeniae by its smaller size, its more numerous costae (19–20 instead 14–15 on the last whorl), only two rows of nodules on the spire (subsutural and shoulder nodules) and in having rounded nodules instead crenulations on the last whorl. From the Lakhra Formation at Jhirak, Vredenburg (1923) described a species rather similar to A. (V.) burtoni , A. (V.) victoriae ( Vredenburg, 1923) . The type specimen, illustrated as Vredenburg’s (1923) pl. 15, fig. 4, is designated here as the lectotype, but it is poorly preserved and it seems only wider than specimens of A. (V.) burtoni . Thus, it is difficult to evaluate whether it corresponds to a variation of A. (V.) burtoni or a distinct species. Cox (1930) described a comparable species, A. (V.) daviesi ( Cox, 1930) from the Paleocene of the Hangu Formation. The rounded aspect of the nodules of A. (V.) daviesi recalls the European Bartonian species A. (V.) digitalinus , but A. (V.) daviesi differs from A. (V.) burtoni by having two abapical spiral rows of nodules below the shoulder row. A. (V.) soriensis ( Eames, 1952) from the Early Eocene of the Zinda Pir section (Western Punjab, Pakistan; Eames 1951b) displays numerous similarities to A. (V.) burtoni , such as rounded nodules, only two rows of nodules (the subsutural and shoulder rows), around 15–19 costae, small size and a biconic shape. In view of these similarities, we consider that A. (V.) burtoni and A. (V.) soriensis could belong to the same species.

Stratigraphic range. Bara Formation (this paper); Lakhra Formation ( Cossmann & Pissarro 1909; Vredenburg 1923);? Ghazij Formation (Punjab).

Figures

FIGURE 9. A – G. Athleta (Volutocorbis) burtoni Vredenburg, 1923, A (CPAG. RAN. I. 31, dorsal view, stn 2), B (CPAG. RAN. I. 32, ventral view, stn 3), C (CPAG. RAN. I. 33, dorsal view, stn 1), D – F (MNHN. F. J 13433, Cossmann coll., ventral (D) and dorsal (E) views, enlarged view of the spire (F), Jhirak), G (MNHN. F. J 13434, Cossmann coll., dorsal view, Jhirak); H – L. Athleta (Volutocorbis) cf. wynnei Cox, 1930, H – I (CPAG. RAN. I. 35, dorsal view (H) and enlarged view of the spire (I), stn 4), J (CPAG. RAN. I. 36, ventral view, stn 4), K – L (CPAG. RAN. I. 34, ventral (K) and dorsal (L) views). Scale bars: A – E, G – H, J – L = 10 mm; F, I = 5 mm.