Mitreola brohii

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 : 107-108

Mitreola brohii sp. nov.

( Fig. 4 B–H)

Etymology. Dedicated to Professor Imdad A. Brohi, Centre for Pure and Applied Geology, University of Sindh, Jamshoro, Pakistan.

Type locality. Stn 4: Lakhra Dome, Lakhra village section, base of the Lakhra Formation.

Type material. Holotype (stn 4, CPAG.RAN. I.2; cast MNHN.F. A50340 ), paratype 1 (stn 4, CPAG.RAN. I.3; cast MNHN.F. A50341 ), paratype 2 (stn 4, CPAG.RAN. I.4; cast MNHN.F. A50342 ), paratype 3 (stn 4, CPAG.RAN. I.5; cast MNHN.F. A50343 ).

Other material. 23 spm (stn 4, MNHN).

Description. Shell ovately fusiform, H 30–33, D 11–14.5 mm (holotype H 31.5 not complete, D 13.9 mm). Protoconch not preserved. Teleoconch of 7–8 whorls. Spire high, occupying 36% of total shell height. Spiral whorls slightly convex. Last whorl rather narrow. Suture linear. Axial sculpture of coarse costae, tending to disappear on penultimate whorl. Costae straight, orthocline, reaching from suture to suture on spire. On first whorl: 12 costae; from second to sixth whorls: 10 to 11 costae; last whorl: no costae. Spiral sculpture of ca. 10–15 fine threads, present only on four earliest whorls. On last whorl, very fine threads on base of aperture. Aperture lenticular, elongate, occupying 63% of total height, 36% of diameter. No posterior notch. Outer lip thin, not thickened externally. Inner lip bearing a callus developed more anteriorly than posteriorly. Four strong columellar folds, the anteriormost oblique. Siphonal canal short, slightly curved dorsally. Siphonal notch shallow, siphonal fasciole poorly developed.

Comparisons. According to Darragh (1985, 1988), Mitreola is a Tethyan genus during the Middle Eocene and its range extended from Australia to the Eastern Atlantic (Europe). However, no species of Mitreola has been recorded between Australia and the western Tethys and, therefore, this record of a species of Mitreola from the Earliest Eocene of the Eastern Tethys fills this gap. M. brohii displays the usual characters of Mitreola as well as atypical characters. An elongate, lenticular aperture with an inner lip bearing four columellar folds, the most basal being oblique, are shared with many species of Mitreola . Coarse costae (e.g. M. raricosta ( Lamarck, 1803) and M. maxwelli Le Renard, 1994 from the Lutetian of the Paris Basin) or a lack of axial sculpture (e.g. M. labratula ( Lamarck, 1803) from the Lutetian of the Paris Basin) are observed in many species of the genus, but the disappearance of the axial sculpture on the last whorls is less frequent. This character of M. brohii is shared only with M. salaputium Darragh, 1988 from the Late Eocene of South–West Australia. M. brohi differs from all other Mitreola species in lacking an externally thickened outer lip, which often bears a variably developed labral nodule ( Cernohorsky 1970; Cate 1972). These authors and Darragh (1988) regarded the presence of a labral nodule as a diagnostic character of the genus, but some species of Mitreola (e.g. M. labratula ( Lamarck, 1803) , M. mutica ( Lamarck, 1803) and M. subplicata (Deshayes, 1835) from the Lutetian of the Paris Basin, France) lack a nodule.

Stratigraphic range. Lakhra Formation: Lakhra Dome.

Figures

FIGURE 4. A. Lyria sp., CPAG. RAN. I. 1, stn 5; B – H. Mitreola brohii sp. nov., B – C (holotype, CPAG. RAN. I. 2, ventral (B) and dorsal (C) views, stn 4), D (paratype 1, CPAG RAN. I. 3, ventral view, stn 4), E – F (paratype 2, CPAG. RAN. I. 4, ventral (E) and dorsal (F) views, stn 4), G – H (paratype 3, CPAG. RAN. I. 5, juvenile, ventral view (G) and enlarged view of the spire (H), stn 4); I – K. Lyriopsis cossmanni (Vredenburg, 1923), I – J (CPAG. RAN. I. 6, ventral view (I) and enlarged view of the spire (J), stn 4), K (CPAG. RAN. I. 7, ventral view, stn 4); L. Lyrischapa haimei (d’Archiac & Haime, 1853), CPAG. RAN. I. 8, ventral view, stn 6; M – N. Lyrischapa sismondai (d’Archiac & Haime, 1853), M (CPAG. RAN. I. 10, ventral view, stn 6), N (CPAG. RAN. I. 9, dorsal view, stn 3). Scale bars: B – G, I, K – N = 10 mm; A, H, J = 5 mm.