Abrachlamys toolinnensis 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, figs. 1-67. [p. 39, figs. 8A, C, E]
2001 Abrachlamys toolinnensis Beu & Darragh, 2001
A. G. Beu, A.G. & T. A. Darragh. 2001, figure 8.
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«Description. Moderate-sized (to c. 39 mm high and 40 mm long), length slightly greater than height in moderate-sized to large specimens, shape acline in most specimens, very weakly prosocline in a few; umbonal angle c. 115º in large specimens; posterodorsal margin similar in length to anterodorsal margin, but inclined ventrally at a slightly steeper angle, posterior auricles therefore a little taller than anterior auricles. Radial sculpture of 28-30 moderately elevated, moderately wide, roundtopped costae, each interspace the same width as one costa; most costae undivided over whole height of most specimens, but a few costae subdivided into extra costae on some specimens, where they rise in prominence to equal primary costae by valve margin; increase is by rib-flank bifurcation on LV (Fig. 8D; one bifurcation clearly visible at posterior third of disc length) and by medial intercalation on RV, although less common on RV than on LV. Disc flanks low, steep (ie., narrowly rounded), with many narrow, closely spaced radial costellae. Commarginal sculpture of low lamellae, c. 1 mm apart over centre of LV disc, elevated slightly to form low scales on costal crests, but very low and straight across costal interspaces, present over entire LV, but on RV present only on auricles and on 2-3 narrow costae on anterior and posterior ends. Entire surface, where not more coarsely sculptured, bears fine, closely spaced antimarginal ridgelets only. RV anterior auricle long and narrow, with deep, wide byssal notch persisting in adults; byssal fasciole depressed, its outer margin inclined dorsally towards posterior so that auricle narrows posteriorly; presumably with functional ctenolium, but teeth not observed; main outer face sculptured with 4-5 prominent, scaly radial costae as on disc; commarginal lamellae raised into prominent, thin serrations along dorsal margin of both RV auricles. LV anterior auricle moderately tall, sculptured as on disc, with weakly sinuous anterior margin inclined moderately strongly towards anterior and dorsum. Posterior auricles moderately tall, sculptured as on disc, posterior margin of both slightly concave, inclined slightly.
Dimensions.
Type material. Holotype, WAM 68.348, Abrakurrie Limestone, Longfordian, cliff face at Toolinna, south of Caiguna, Eucla Basin, Western Australia, coll. P. J. Bridge, 1967; this is the only specimen of Abrachlamys toolinnensis sp. nov. that has been collected weathered out on an exposure, rather than removed from a block of hard limestone, and so is by far the most suitable specimen to be the holotype. Li et al. (1996) identified the limestone at Toolinna Cove as Abrakurrie Limestone, based on foraminiferal biostratigraphy, and this assignment is confirmed by the very close similarity of the holotype of A. toolinnensis to specimens from more inland outcrops. James & Bone (1994) had earlier mapped ‘Oligocene-Early Miocene’ Abrakurrie Limestone reaching a thickness of more than 30 m at Toolinna Cove, and showed pectinids (apparently A. toolinnensis) occurring abundantly in outcrop (James & Bone 1994: fig. 8a). WAM 78.3951, Abrakurrie Limestone, roof fall in eastern extension of Mullamullang Cave, Madura district, southeastern Western Australia, coll. G. W. Kendrick, 21.V.1978, 6 paratypes removed from a block of firm, yellow limestone; WAM 78.3952, Abrakurrie Limestone, all data as for WAM 78.3951, 2 paratypes and c. 12 less complete specimens removed from a block of firm yelloworange limestone, plus numerous fragmentary specimens remaining in pieces of rock; WAM 99.499, Abrakurrie Limestone, spoil from well at ruin, Moodini Bluff, 23 km E of Madura Roadhouse, at foot of Hampton Escarpment, Madura district, southeastern Western Australia, map ref. Madura 530054, coll. T. A. Darragh, M. Archer, G. W. Kendrick, 5 .iii.1969; 2 paratypes and 3 fragmentary specimens removed from a block of hard, cream-fawn limestone. These specimens were removed from the same block as the type material of Talochlamys multilamellata sp. nov.
Occurrence and time range. Known only from Abrakurrie Limestone (Longfordian), Eucla Basin, southeastern Western Australia
Remarks. The distinctive combination of characters seen in Abrachlamys toolinnensis gen. nov., sp. nov., will make it easily recognised, and there are really very few pectinids from Australia or New Zealand it can be compared with. As noted above, Dr T. R. Waller (1999, pers. comm.) has indicated that many European and eastern North American Eocene and Oligocene pectinids closely resemble A. toolinnensis, eg., ‘Pecten’ plebeius Lamarck, 1806 (illustrated, as Lyropecten (Aequipecten) plebeius, by Glibert 1976: 40, pl. 2, fig. 4a, b), and it is likely that this is a widespread Paleogene genus-group. ‘P.’ plebeius is much less scaly than A. toolinnensis sp. nov., and seems to lack the discrepancy between the valves in scale development that is so characteristic of the present species. A. toolinnensis occurs in Abrakurrie Limestone with Talochlamys multilamellata sp. nov., and some of the paratypes and other specimens listed above were removed from the same block as all the known material of T. multilamellata. They were immediately separable while being removed from the rock, because of the slightly greater inflation of A. toolinnensis, the lack of commarginal sculpture over almost all of the RV of A. toolinnensis, compared with consistent commarginal lamellae on both valves in T. multilamellata, and the much more frequently and finely subdivided radial costae, and the resulting much frillier sculpture in general, of T. multilamellata. The fixed number of radial costae, or at most with a few costae very weakly subdivided on a few specimens, the persistence of antimarginal ridgelets across the entire RV, the wide, aequipectinoid shape which, however, retains a deep byssal notch in the largest specimens seen, the thin and fragile shell, and the widely spaced, rather prominent commarginal lamellae on the LV but its absence over most of the RV are the diagnostic characters of the new genus and species.
Etymology. The specific name ( ‘from Toolinna’) refers to the type locality of the species, Toolinna Bluff.»
ALAN GLENN BEU & THOMAS ALWYNNE DARRAGH, 2001
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