Talochlamys badioriva Beu & Darragh, 2001
BEU, A. G. & T. A. DARRAGH. 2001. Revision of southern Australian Cenozoic fossil Pectinidae (Mollusca: Bivalvia). Proceedings of the Royal Society of Victoria, 113: 1–205 [p. 97, figs. 30A-I, 31A, D, F,H, 32AC]
2001 Talochlamys badioriva Beu & Darragh, 2001
A. G. Beu & T. A. Darragh, 2001, figure 30.
A. G. Beu & T. A. Darragh, 2001, figure 31.
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«Pecten peroni Tate, 1886: 108 [in part; unfigured paralectotypes from Adelaide (= Kent Town) Bore only].
Description. Moderate-sized for genus (to c. 35 mm high), slightly taller than long (when small) to slightly longer than tall, umbonal angle 105-110º in adults; RV slightly more inflated than LV; acline to weakly prosocline. LV preradial dissoconch sculptured with antimarginal ridgelets and low but obvious commarginal ridges, forming tessellate sculpture and shallow, elongate pits more prominent than in T. pulleineana but less so than in T. dichroa. Disc sculpture of 26-32 moderately narrow, well elevated radial costae with rounded crests; most specimens developing narrow secondary costa on each side of each primary costa, commencing at valve height of 10-12 mm, to produce regular pattern of weakly fasciculate costae on distal half of disc of large specimens, although some costae remain undivided on others; some secondary costae subdivide more strongly to become separate narrow costae in intercostal space; low, narrow tertiary costellae intercalated in centre of radial interspaces at half valve height to near ventral margin of some large specimens, one costella in most interspaces of most specimens but up to 3 in some interspaces. Much or all of shell surface sculptured with fine antimarginal ridgelets, which are subdivided into groups of short, weakly radiating ridgelets between commarginal growth ridges over distal area of disc that bears subdivided primary costae. Commarginal ridges over proximal area of radially sculptured disc (after costal inception but before costal subdivision) raised into thin lamellae of shallow V-shape with edges of V lightly concave ventrally; after costal subdivision lamellae become lower or disappear on floor of interspaces, but become elevated into high, thin, ventrally concave but outward-curved scales, with separate longer, wider scales on primary costae and shorter, much narrower ones on secondary costae. RV anterior auricle with very deep, moderately narrow byssal notch, functional ctenolium with 4 -6 narrow teeth, depressed, strongly ridged byssal fasciole, and main auricular surface above byssal fasciole sculptured with 5-6 prominent, very scaly costae; LV anterior auricle tall, anterior margin lightly convex and inclined strongly towards anterior, sculptured with 6-7 narrow, finely scaly costae; posterior auricles short, with concave posterior outline, sculptured with 3-5 narrow, widely spaced, finely scaly costae; dorsal margins of RV auricles strongly serrate. Interior smooth apart from weakly notched ventral margin. Hinge with long, low, thin dorsal teeth and short, very narrow resilial teeth beside dorsal half of resilifer.
Type material. Holotype, NMV P301355, paired valves, PL3011, Browns Creek Clay (Aldingan), 10 m below greensand bed, washout nearest Browns Creek, Johanna coast of southern Victoria, map ref. Glen Aire 079058, coll. T. A. Darragh, 28.x.1971; paratype, NMV P302792, LV, all data as holotype; paratype, NMV P301513, RV, PL3011, locality as above, coll. T. A. Darragh, 29 .xi..1972; paratypes NMV P304574-5, LVs, locality as above, coll. T. A. Darragh, 24.ii.1971.
Other material examined. Aldingan: BROWNS CREEK CLAY: PL3011, Browns Creek (36 specimens); PORT WILLUNGA FORMATION: SAM T930F (1 specimen; one of Tate’s unfigured paralectotypes of Pecten peroni, ‘polyzoal limestone, Aldinga Bay’); PL30I0, Blanche Point (2 specimens); PL3612, bore 240, Klemzig, SA (10 specimens); NANARUP LIMESTONE: WAM, PL506, Nanarup lime quarry (15 specimens); PANILLUP SILTSTONE: WAM 63.76, Woogenellup, via Mt Barker, WA (1 specimen); WAM 70.1813, crossing of Bremer River, 14km NW of Bremer Bay township, WA, map ref. Bremer Bay 223 761 (1 specimen); WAM 71.216, near Hunter River mouth, 200 m from beach, Bremer Bay district, map ref. Cheyne Beach 240 754 (1 specimen); WAM 76.1230, beside dam 3.2 km E of Lort River, 0.8 km N of Albany-Esperance Rd, WA (1 specimen); WAM 85.36, gully by main road, Bremer Bay townsite, WA (1 specimen, part and counterpart); WAM 86.472, Mettler Lake Nature Reserve, WA (1 specimen). Occurrence and time range. Apparently restricted to Aldingan (Late Eocene); recorded widely across southern Australia: Browns Creek, Johanna, Victoria; Adelaide bores and Aldinga Bay, South Australia; Nanarup Limestone and Pallinup Siltstone in southern Western Australia. Remarks. This new species is closely similar to T. keiloriana in most characters and makes a very plausible direct ancestor for that species. T. badioriva sp. nov. differs from T. keiloriana in its smaller maximum size, its much more prominent LV preradial dissoconch sculpture, with obvious commarginal ridges and antimarginal ridgelets surrounding the pits (rather than merely extremely shallow, elongate pits as in T. keiloriana), and in a much higher proportion of specimens (up to c. 80% of the well preserved Browns Creek Clay specimens) having the finely subdivided costae and intricately frilled costal scales, which give this species group a distinctive appearance but which are seen on only perhaps 30% of specimens of T. keiloriana, and are still more elaborated in T. multilamellata. The shallowly V-shaped commarginal lamellae on the disc after costal inception but before costal subdivision are seen weakly on only a few specimens of T. keiloriana, but are present on most well preserved specimens of T. badioriva. These V-shaped commarginal lamellae were initially considered by us to be possible homologues of those illustrated on Aequipecten opercularis (Linne) by Waller (1991: pl. 4, fig. 9) and stated by Waller (1991; 32) to be characteristic of the Tribe Aequipectinini. However, SEM examination of A. opercularis showed that the ventral flexure of the commarginal lamellae in Aequipecten is quite different in shape and formation from that of Talochlamys, and Aequipecten differs further in having extremely coarse, deep, simple, circular pits on the LV preradial dissoconch, and prominent internal rib carinae. The resemblance in commarginal lamellae is therefore another convergent character. Natural moulds of the exterior of small, finely sculptured pectinids in Pallinup Siltstone from southern Western Australia were studied by SEM as silicone rubber impressions, and showed enough sculptural detail (Fig. 31A, D, F, H) in common with the well preserved shells from Browns Creek for a positive identification as T. badioriva. Etymology. The specific name (Latin, ‘badius’, brown + ‘rivus’, stream) refers to the type locality of the species, Browns Creek.» ALAN GLENN BEU & THOMAS ALWYNNE DARRAGH, 2001
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