Tertiary Research 21 (1-4) 1-10 3 Plates, 1 text-fig. Leiden November 2002 The Neritidae of the Barton Group (Middle Eocene) of the Hampshire Basin. MALCOLM F. SYMONDS Abstract: Gastropods of the family Neritidae in the Eocene Barton Group of the Hampshire Basin, southern England are reviewed and three previously undescribed taxa are described. New species: Nerita (Amphinerita) bartonensis and Theodoxus (Pictoneritina) waltoni. New subspecies: Theodoxus (Pictoneritina) passyanus denslatus. New combination and amended diagnosis: Theodoxus globosus (J. de C. Sowerby, 1823). Neotype designated for Nerita globosa J. de C. Sowerby, 1823. Amended diagnosis: subgenus Amphinerita. Amended diagnosis: subgenus Pictoneritina M. F. SYMONDS The Cottage in the Park, Ashtead Park, Ashtead, Surrey KT21 1LE, UK Accepted: 20th September 2001 INTRODUCTION Formation, from the condition and matrix, probably Bed A3 The family Neritidae is poorly represented in the Barton of Burton (1933). Group but rare examples do occur in at least three horizons, Locus typicus: Highcliff, Hampshire. namely beds A3, E and F of Burton (1933) but these have not been described in any detail. Examination of the Paratypes: BMNH GG22556 (H. Eliot Walton coll.), (Pl. 1, material in the Department of Palaeontology, The Natural fig. 3), BMNH 3414 (Pl. 1, fig. 4), BMNH 3414 (Pl. 1, fig History Museum, London (hereinafter called: “BMNH”) has 5). shown several taxa to be present including two new species Diagnosis: A rather small Amphinerita with a smooth and a subspecies which are herein described. The operculum exterior to the shell, the initial whorls, but not usually the is often of importance in the classification of the Neritidae last whorl, covering the spire. The septum surface has but unfortunately no operculum has yet been found, as far as irregular folds and its edge is denticulate. The outer lip is I am aware, in the Barton Group. smooth within. Description: The shell is rather small, ovate in the adult Family NERITIDAE Rafinesque 1815 stage, juveniles are broadly ovate in adapatural view. Genus NERITA Linné 1758 Juveniles are thin shelled but in the adults the outer lip is substantially thickened and bevelled at the edge. The initial Type species, by subsequent designation, Montfort, 1810: whorls are completely obscured by the immediately Nerita peloronta Linné 1758. Recent, marine, Caribbean. succeeding whorls, which are entirely convex, but in some adults, including the holotype, the last whorl is slightly concave just below the suture and it does not obscure the Subgenus AMPHINERITA Martens 1887 penultimate whorl leaving a slightly excerted spire. Type species, by subsequent designation, Baker, 1923: The external surface is polished and smooth except for fine, Nerita umlaasiana Krauss, 1848. Recent, marine, South transverse, growth lines. The colour pattern is fairly Africa. constant consisting of two or three prominent, continuous, solid, whitish, spiral bands; these are interspersed with spiral Diagnosis (Keen in Knight et al., 1960: 1282): Smooth or strips, often of approximately similar width to the whitish finely striate, oblique; labial area smooth, margin weakly bands but much broader in some specimens, brown in colour dentate. with white spots. Remarks: Martens’ description is brief and of little The aperture is slightly oblique and semilunar. The septum assistance (Martens, 1887-9: 9) and I have used that given is broad with irregular folds and/or pustules in the centre of by Keen which appears to be based mainly on the the upper surface. The central half of the septum edge is characteristics of the type species. N. umlaasiana is also distinctly concave. The dentition consists of a series of characterised by a thickened outer lip which is smooth small, regular teeth, up to eight in number, which occupy the within, lacking any teeth or striations. However, although concave central section. A very slight upper tooth, the septum surface is generally smooth in N. umlaasiana, it immediately adapical to the concave section, is also present is certainly not so in Nerita atrata Chemnitz, 1781 (= Nerita in a few specimens. The outer lip is smooth within. There is senegalensis Gmelin, 1791) which Martens included in his a small, conoidal, apertural tooth below the abapical end of subgenus Amphinerita. the septum. Size: Height 10mm, width 7.6mm (holotype). Nerita (Amphinerita) bartonensis sp. nov. Remarks: The colour pattern of N. bartonensis is Pl. 1, figs 2-5 superficially similar to that of some specimens of Theodoxus passyanus (Deshayes, 1864) and this may be the reason for it Derivatio nominis: Named after the Barton Group from having been overlooked as a separate taxon. However the which all the known specimens have come. whitish bands on N. bartonensis are solid and continuous Holotype: BMNH 73209 (F.E. Edwards coll.). An adult of whereas in those specimens of T. passyanus which are average size. (Pl. 1, fig. 2) banded the bands are not always continuous and they are not solid but rather a concentration of white spots. The Stratum typicum: “Lower Barton Beds”; Barton Clay morphology of the two species is very different: juvenile N. 2 SYMONDS bartonensis can be readily separated by the spire being Amended diagnosis: The material from the Barton Group obscured by succeeding whorls and the adults by the thick, at BMNH includes a single broken specimen, the neotype, bevelled outer lip. which matches closely the description and illustration in Sowerby although what Sowerby describes as “a very Range and distribution: I have not found this species in obtuse tooth” near the upper end of the septum appears in the collection of the Muséum National d’Histoire Naturelle his accompanying figure (see Text-fig. 1) and in the in Paris (hereinafter called: “MNHN”) and it appears to be neotype more as a slight swelling of the adapical end of the confined to the Barton Group of the Hampshire Basin. Five septum edge than as a parietal tooth in the usual sense. specimens which have detailed provenance (BMNH Pal. TG 18286-18290 D. Curry coll.) are from bed A3 of Burton In addition to Sowerby’s description of the holotype, the (1933). Others are labelled “Highcliff” and it seems likely following details are apparent from an examination of the from the state of preservation that most, if not all, are from neotype. The whorls are evenly rounded and convex except bed A3. for a conspicuously concave section immediately below the suture; the suture itself is prominent and quite deep but this could be due to the worn condition of the neotype. The Genus THEODOXUS Montfort 1810 surface is covered by approximately 25 evenly spaced, low, rounded, fairly even sized, spiral ridges separated by Type species, by original designation: Theodoxus lutetianus narrow, shallow grooves, the ridges becoming flattened and Montfort 1810 ( = Nerita fluviatilis Linné 1758). Recent, less conspicuous on the upper half of the last 10mm or so of freshwater, Europe. the final whorl; the spiral ridges are crossed by a few prominent growth lines interspersed by very fine, close, Diagnosis (Keen in Knight et al., 1960: 1285): Small, transverse lines. The “lamelliform tooth” within the obliquely ovate, spire low or elevated; labial area smooth, aperture, noted by Sowerby and clearly visible in plate 1, with smooth or dentate margin; operculum smooth. figure 1a, consists of two raised ridges which meet to form two sides of a triangle with the open end towards the aperture and the apex pointing into the interior of the shell; Theodoxus globosus (J. de C. Sowerby 1823), comb. the inner ridge is longer than the outer one and both incease nov. in height as the apex is reached. The colour pattern consists of a dark brown background with white dashes and spots Pl. 1, fig. 1 and three whitish, spiral bands. Nerita globosa J. de C. Sowerby, 1823: 5: 29, pl. 424, fig. Size: Height 18.2mm, width 13.8mm (neotype). 1. (Text-fig. 1). Remarks: Accordingly to Sherborne (1926, 2733), Diagnosis: The shell is subglobose, transversly sulcated; Férussac described a Nerita globosa at an unspecified date the spire is apparent; there is one tooth on the septum; the between 1800 and 1850 in his Histoire naturelle générale et outer lip is plain within. particulière des Mollusques, pl. Nerites fossiles, fig. 14. Type and locus typicus: The holotype was lost in the 19th Also, Keen in Knight et al. (1960, 1284) refers to Nerita century according to a manuscript note, “missing June globosa Férussac, 1823. However fig. 14 of the relevant 1889”, alongside the figure of the holotype in the copy of plate shows Nerita globulus (= Neritoplica uniplicata (J. de The Mineral Conchology of Great Britain in the Cox C. Sowerby, 1823) Wenz, 1938). The folio edition of this Library, the Department of Palaeontology, BMNH. A work in the Mollusca Library, BMNH, omits the name of recent search of relevant parts of the BMNH collection has the species shown in fig. 14, presumably due to a printing failed to reveal any trace of the holotype. The type locality error. Kennard (1942, 15) states that the caption for fig. 14 is not clearly specified but is apparently Hampshire since was “Nerita globulus”. He also gives the date for Sowerby’s description was based on a unique specimen lent publication of Férussac’s livraison 20, which includes the th by the Rev. T. Cooke “who has taken much pains to fill up Nerites fossiles plate, as 27 September 1823. Cleevely our list of Hampshire shells”. No other information is (1974, 444) puts the date of publication of Sowerby’s st given as to the locality of the holotype but Sowerby description of Nerita globosa as 1 August 1823. remarked that it contained two valves of Corbula pisum, Accordingly, regardless of whether Férussac used the which indicates that the holotype could well have come specific name globosa or globulus, Sowerby’s description from the Barton Group.