Lanistes tricarinatus, Neubert & Damme, 2012

Neubert, Eike & Damme, Dirk van, 2012, Palaeogene continental molluscs of Oman, Contributions to Natural History 20, pp. 1-28 : 6-8

Lanistes tricarinatus sp. nov.

( Figs. 5–6 )

Type specimens: Holotype NMBE 5018963 ; paratypes NMBE 5018964–5018965 , 5019037 .

Type locality: Wadi Darbat , Dhofar, Oman.

Stratum typicum: Paludal biomicritic limestones of the Zalumah Formation.

Age: Late Priabonian.

Material: This species probably occurs in most exposures of the Zalumah Formation. The material here described was collected in 2012 by both authors in the Wadi Darbat area .

Etymology: Named after the three carinae on the third whorl.

Diagnosis: A palaeogene species of Lanistes of the L. carinatus type, i.e. characterized by a depressed shell with a peripheral carina on the upper whorls and a very large open umbilicus. Such shells were formerly ranged in the subgenus Lanistes s.str. ( Mandahl-Barth 1954).

Description: With a diameter of 77.3 mm this is the largest Lanistes species known, but most specimens do not exceed 60 mm. Depressed shell consisting of 5 ¾ rapidly increasing whorls; spire little exserted, apex blunt; first whorl smooth, second whorl with two sharp keels at the base and the top of the periphery respectively, third whorl with one keel at the base and a double keel at the top, the upper part of these whorls sunk below the rim formed by the upper keel or keels; fourth whorl evenly rounded, except for a faint central keel; surface smooth, marked with growth-lines only, no spiral sculpture visible; aperture acuminate ovate, pointed at the base, outer margin evenly curved, umbilical margin straight; umbilicus wide, deep and funnel-shaped, bound by a strongly thickened and slightly raised angle; operculum unknown.

Measurements: Holotype ( Fig. 5 ): H = 45.8 mm; W = 77.3 mm, h = 42.2 mm; w = 34.0 mm; Paratype NMBE 5018965: H = 34.8 mm; W = 49.2 mm; h = 30 mm; w = 23.3 mm.

Remarks: The record by Roger & al. (1994) of Lanistes subcarinatus (nomen nudum) in their geological study of the Dhofar region seems to pertain to this species. It is the most common of the few fresh water snails present in the Zalumah Formation. In large specimens the apex is strongly eroded and the carination no longer visible.

The Palaeogene fossils mentioned from Egypt and Sudan, namely L. antiquus MAYER-EYMAR, 1893 ; L. olivieri MONTFORT, 1810 , and L. sodaensis ABBASS, 1967 ( Abbass 1967) and L. grabhami COx, 1933 , redescribed by Gautier (1973) have all the same L. carinatus morphology. They do differ from L. tricarinatus sp. nov. by their smaller size. But these fossils are badly preserved (mainly inner moulds) and the ornamentation on the first whorls is not visible. It hence cannot be excluded that some of that NE African material may pertain to L. tricarinatus .

Figures

Figs. 5–6: Lanistes tricarinatus sp. nov. Fig. 5: Wadi Darbat, holotype NMBE 5018963 in frontal, apical and ventral view. Fig. 6: Parataype NMBE 5018964 showing a specimen with the carinae.