The Beagle. Keeonis of the Northern Territory Museum of Arts and Sciences. 1991 8( 1); 169-188 CAMBRIAN FAUNA OF THE TOP SPRINGS LIMESTONE, GEORGINA BASIN. PETER D. KRUSE Northern Territory Geological Survey, PO Box 2901, Darwin NT 0801, Australia. ABSTRACT The Top Springs Limestone, a carbonate unit of the northern Georgina Basin, Northern Territory, Australia, has previously yielded only the trilobite Redlichia. indicating an Ordian (early Middle Cambrian) age for at least part of the formation. New collections of trilobites. brachiopods. hyoliths, molluscs and .sponges - fifteen species in ail - are described here, leading to the po.ssibility that upper parts of the formation may have been deposited during the succeeding early Templetonian stage. The fauna has a clear affinity with that in the Tindall Limestone of the Daly Basin, and toa lesserextent with the Panton Formation fauna of the Ord Basin. The new helcionellid molluscan genus Kutanjia ngalhalct and new species Igorella ditrara are also described. Keywords: Cambrian, Northern Territory, Georgina Basin, Trilobita, Brachiopoda, Hyolitha, Mollusca, Porifera. INTRODUCTION forresti from the vicinity of Top Spring home¬ stead, prompting an Ordian (early Middle The Top Spring.s Lime.stone is a flat-lying Cambrian) age assignment for the Top Springs Cambrian carbonate unit in the notlheastem North¬ Limestone. ern Territory, occupyitig portions of the Bauhinia Recent regional mapping of the Bauhinia Downs Downs and Wallhallow 1:250 000 map sheet sheet area by the Northern Territory Geological areas (Smith 1964; Plumb and Rhodes 1964). In Survey (Pietsch et al. 1991) was accompanied by outcrop it generally rests w'ith probable palaeontological sampling of the Top Springs di.sconformity on the Bukalara Sandstone (Dunn Limestone throughout its outcrop area and in 1963), which I'tcars the vertical dwelling burrow drillhole DD83SC-1 (Fig. 2). As a result, in Skolithos throughout and is thus regarded as Early addition to the Redlichia, a suite of inarticulate Cambrian in age. These two units together repre¬ and articulate brachiopods, hyoliths, molluscs, sent the northernmost extension of the Georgina sponges, sponge spicules, chancelloriides, Basin: connections with the remainder of the echinodenn ossicles and problematic tubes has basin are ob.scured by Cretaceous cover (Fig. I). been collected. The trilobites, brachiopods, Where the Bukalara Sandstone is absent, the hyoliths, molluscs and sponges are described Top Springs Limestone mantles Middle here, and together demonstrate a clear affinity Proterozoic rocks of the McArthur Basin. To the with the undoubtedly coeval fauna of the Tindall south it is unconfonnably overlain by Cretaceous Limestone in the Daly Basin (Kruse 1990). deposits. Cored drillholes DD83SC-I and Redlichia forresti and Gtidugiiwan hardmani are DD86SC-2 (CoHiver 1984), in the Wallhallow also shared with Ihe Panton Formation in the Ord sheet area, commenced in Cretaceous rocks and Basin (Table 1). intersected a minimum of 80 m and 92 m of Top Although Redlichia, characteristic of the Ordian Springs Limestone respectively before entering stage in northern Australia, is the only trilobite vesicular basalt (Antrim Plateau Volcanics equiva¬ pre.sently known from the Top Springs Lime¬ lent) beneath. These drillholes represent the maxi¬ stone, other elements of the fauna such as mum known stratigraphic thickness of the unit. Microniitra nerranuhawn and Diraphora sp. sug¬ Opik (in Randal and Nichols 1963. Appendix gest a slightly younger age. as in the Daly Basin I) reported a species of Redlichia close to R. their stratigraphic range is restricted to the upper. 169 Peter D. Kruse 129"E 132"E 135’E I38’E early Templetonian interval of the Tindall Lime¬ coquinas), brecciated limestone, pink to pale brown stone. However, M. nerranuhawu has since been cryptomicrobial laminite and rare grey fenestral reported from the Coonigan Formation of western limestone. Patchy or fabric-selective brown New South Wales (Roberts and Jell 1990), where silicification is common at surface; preferentially it co-occurs with Redlichia and is therefore Ordian. silicified components include individual The Top Springs Limestone is a part of the cryptomicrobial laminations, onkoids and bioclasts. unconformity-bounded Ordian-early Temple¬ Contrary to the original drill log interpretation tonian sediment package recognised elsewhere in (Colliver 1984: 7), palaeontological sampling has the Georgina basin by Shergold et al. (1988). established that the entire cored supra-basall in¬ The Top Springs Limestone was introduced by terval in drillholes DD83SC-I and DD86SC-2 is Plumb and Rhodes (1963, 1964) and defined by Top Springs Lime.stone. The cryptomicrobial Kruse (in Pietsch et al. 1991). Grey, partially laminites constitute the basal 3-9 m of the forma¬ dolomitised mottled and onkoid limestone are tion: these are locally exposed around Rocky and prominent in outcrop, with minor grey bioclastic Black Springs Creeks and in the bed of the limestone (in places as silicified hyolith-brachiopod McArthur River in the northern Wallhallow sheet 170 Top Springs Limestone 135‘30E 136’OOE 17'00'S 135'30E 136'OOE Undifferentiated Cretaceous and • 190988 Fossil locality with AMG coordinates overlying Cainozoic A DD83SC1 Cored drillhole Top Springs Limestone m Kiana Homestead Precambrian and Lower Cambrian CLYDE 1: too 000 map sheet Fig. 2. Geological map of the Top Springs Limestone showing fossil localities. The Bauhinia Downs and Wallhallow 1:250 000 sheet areas are respectively north and south of 17°00’S. area (Fig. 3A). They range from selectively cecded by a variety of grey limestone types. dolomitised millimetre-scale sedimentary lami¬ Occurrences of anhydrite suggest an evaporite nations through to more finely crcnulated laminites solution-collapse origin for brecciated limestone wherein micrite or microspar cryptomicrobial intervals. laminations alternate with more thrombolitic In thin section, the dominant mottled lime¬ cryptomicrobial intervals. stones are identified as bioclastic wackestones The,seunfossiliferouscryptomicrobial laminites (Fig. 30, with hyolith, trilobite and brachiopod are immediately succeeded by cryptomicrobial fragments in a bioturbated, patchily dolomitised boundstone or packstone (Fig. 3B), in turn sue- micrite-peloid matrix. These grade into onkoid wackestones (Fig. 3D) as bioclasts (particularly Tabic I. List of Top Springs Limestone fauna (at left), together with (at right) hyoliths) are progressively coated by Girvanella. occurrences in common with the Tindall Limestone (Daly Basin) and Panion Grey limestones featureless in hand specimen arc Formation (Onl Basin); o=species in common. 4-sgcnus in common. Note that Panion Formation brachiopods. molluscs and sponges have not been seen under the microscope to be peloid grainstones. studied. Outcrops of all carbonate litliologies are typically TOP SPRINGS LIMESTONE TINDALL PANTON LIMESTONE FORMATION subject to karstification, fomiing pavements, lapies, kamenitza, dolines and towers. TRILOBITES Hedlichia fonrsfi (Etheridge) + 0 Siliciclastic input was minimal. The Top Springs BRACHIOPODS Wesronia ^inapunnensis Kruse o Limestone is an essentially shallow shelf marine Kxrshohaktella muJfJirri Kruse 0 carbonate unit punctuated by one or a few brief HuJrorrcia djugovun Kruse 0 Eolhele nupiii H Kruse 0 peritidal episodes and located away from (seaward Mkroniitru iienunuhawii Kruse o of?) the peritidal siliciclastic sedimentary influences Diraphora -sp. + HYOLITHS affecting the coeval Tindall Limestone to the north¬ GuiJii}:uwan haniniuiii (Etheridge) 0 0 west. MOLLUSCS Lulouchella cf. uirordioiwta Specimens FJ1/6-91/156 tue lodged in the North¬ . Runnegar and Jell o Igorella diiivn/ sp. nov. ern 'Tenitory Museum of Arts and Sciences, Darwin. Kuiuiijh naulhaia gen. el sp. nov. ?cnigrnaconid indcl. Additional specimens are contained in twenty six ?scencliid indet. accompanying unnumbered slides. Collecting lo¬ SPONGES Vawonva sp. 0 calities are specified by an Australian Map Grid lilhistide indet. 0 (AMG) reference and 1:1(X) (XK) map sheet (Fig. 2). 171 Peter D. Kruse Fig. 3. Top Springs Limestone lithologies: A, basal cr>plomicrobial laniinile, AMG 58616.3 KILGOUR; 1$. thrombolilic limestone gradine'upward into cryptomierobial packslonc. AMG 967966 KILGOUR; C. common hyolith-trilobite bioclast wackestone; matrix is micritc with line sand-size pcioids: note cavities geopctally Roored by micritc. silt or bioclasts, AMG 190988 LANCEVVOOD; I). onkoitl-bioclast wackestone-packstone. AMG 190988 LANCEWOOD, All x4. SYSTEMATICS Redlichia forresti (PTheridge in Foord, 1890) (Fig. 4) Class Trilobita Walch Order Redlichiida Richter Olenelliis ? forresti Etheridge in Foord, 1890; Suborder Redlichiina Richter 99-100. pl.4. figs 2. 2a-b. Superfamily Redlicliiacea Foulsen Redlichia forresti - Opik 1958: 12-17, 26-.32. Family Redlichiidae E’oulsen figs 1-.3,7-8,pl.l.figs 1-3,pl.2, figs 1-4, pi.3, figs 1-4. Vtenus Redlichia Cossmann. 1902 ‘species close to Redlichia forresti' - Opik in Randal and Nichols 1963: appendix I. Type species. Hoeferia noetlingi Redlich. 1899 Redlichia forresti - BergsUom 1973: 17. [Middle Cambrian. ¥Khussak Group', Salt Range, Redlichia forresti - McNamara 1986: 405-406. Pakistani. 408-41 1. fig. I A. B, D. F-1. 172 Top Springs Limestone Fig. 4. Kedlichiii fonesli'. A, trimidiiim x3; I!, cranidium P91/7 xIO; C. cranidium Pyi/8 x.^; D. cranidiuni P91/9 x7; K.cranidium P91/I0 x.3; K. cranidium P91/11 x.3; (L free cheek P91/12 x3: H. fused rostral plate and hypostome [’91/13 x.S; I.hypostome I’yi/M x7; .1, pygidium Pyi/L”) x8; K. thoracic segments P9I/I6 x3; L. thoracic segments P9I/I7 x3. All from AMG Sa-MX).-! KII.GOUR. 173 Peter D. Kruse Material. Forty three specimens including over Pygidium small, moderately vaulted. Ante¬ forty cranidia, six free cheeks, three hypostomes. rior segment well defined; second segment six thoracic portions and one pygidium. P91/6- poorly defined. Central portion of pygidium is 91/48 from AMG 86500.5 KILGOUR. a moderately vaulted convexity, without subdi¬ Diagnosis. Exoskeleton smooth except for vision. raised lines on rostral plate and hypostome. Fron¬ Remarks. Redlichia forrcsii belongs to a tal limb narrow, width about 95-1 \0% cephalic cohort of Australian Redlichia species recoe- length, and approximately as wide as fixed cheeks. nised by Opik (1970), also including R. idonea Description. Cranidium 88-102% as long as Whitehouse, 1939 and R. advialis Opik, 1970, wide; largest 22 mm length. Glabella tapering having a relatively narrow frontal limb (100- anteriorly to 65-75% of basal width with rounded 110% of cephalic length) and a smooth to anterior. Axial and glabellar furrows shallow, weakly ornamented cephalon. Opik (1970) re¬ with slightly deeper pits at junctions. SO trans¬ corded the latter two species from the Georgina verse, continuous; SI rarely continuous. LO Basin in western Queensland. Redlichia idonea subcrescentic. is distinguished by its slightly narrower fixed At level of SI, fixed cheeks half glabellar cheeks, with the posterior tips of the palpebral width. Palpebral furrow distinct, of uniform lobes terminating closer to the occipital lobe. In depth and width. Palpebral lobes one-third of R. advialis, each thoracic segment, as well as maximum interocular cheek width. Posteriorly, the occipital lobe, possesses a spine or low palpebral lobes separated from axial furrow by nodal process, whereas in R. forresti, spines gap equal to or slightly greater than width of are pre.sent only on the fourth and twelfth seg¬ lobes. Frontal limb width 95-110% of cephalic ments. Most thoracic .segments in the Top length; subequal to maximum width of fixed Springs Limestone collection lack such proc¬ cheeks. Frontal area length (sag.) 10-30% esses. glabellar length. Preglabellar field represents According to Opik (1970), pygidia of both R. about half of frontal area length in juvenile forresti and R. idonea have attached ankylosed specimens (less than 12 mm length); glabella thoracic segments, but not so R. advialis. How¬ reaches anterior border furrow in larger cranidia. ever, McNamara (1986) mentions ankylosed Anterior borderconvex, of uniform length (sag.) .segments attached to only two of four topotype throughout. Posterior border furrow shallow; pygidia of R. forresti. posterior limbs not exposed. Preocular facial The present compari.son of the Top Springs suture divergent at 55-60° to sagittal line. Limestone fomi with R. forresti is based on the Free cheek rising gently from broad, shallow description by Opik (1958), together with a border furrows to low eye socle. Border convex topotype collection from the Linnekar Lime¬ dorsally. Genal spine advanced, subtending 50° stone of the Ord Basin. The only evident differ¬ between spine and posterolateral border. ences are the median dorsal groove along most, Rostral plate and hypostome fused. Rostral but not all genal spines in Linnekar Limestone plate wide, as long as border, with comarginal specimens (absent in those from the Top Springs terrace lines anteriorly, and a row of 10-12 pits Limestone), and the lack of an ankylosed seg¬ lateral to hypostome on either side (Fig. 4H). ment in the one Top Springs Limestone Corresponding pits are present in anterior bor¬ pygidium available. This latter pygidium is der furrows of .some cranidia. Hypostome with unlike those of R. forresti figured by Opik median body divided by median furrow into (1958), but has the same basic plan as topotype distinct convex anterior lobe and flatter poste¬ pygidia figured by McNamara (1986). rior lobe; median furrow subparallel to poste¬ The terrace lines on the rostral plate and rior border of hypostome. Shallow but clearly hypostomal border of some Top Springs Lime¬ impressed border furrow laterally and stone specimens are paralleled by similar orna¬ posteriorly. Border convex, of uniform width, ment observed on some free cheek and pleural with comarginal terrace lines in some speci¬ doublures in the Linnekar Limestone collec¬ mens. Posterolateral border with two pairs of tion. short marginal spines. The Redlichia sp. from the Tindall Lime¬ Thoracic segments with falcate pleural spines, stone (Kruse 1990) has a relatively wider fron¬ diagonal pleural furrow and, at least in some, a tal limb with longer (sag.) anterior border, and median tubercle. probably represents a separate species. 174 Top Springs Limestone Phylum Brachiopoda Dumeril Westonia ?nyapungensis Kruse, 1990 Class Inarticulata Huxley (Fig. 5) Order Lingulida Waagen Superfainily Lingulacea Menke ? Westonia nyaimngensis Kruse, 1990: 24, fig. Family Obolidae King 13, pl.9 [cum syn.]. Subfamily Lingulellinae Schuchert Material. Six specimens. Pedicle valves P91/ 49-91/51 from AMG 773185 KILGOUR; brachial valves P91/52-91/54 from AMG 773185 Genus Westonia Walcott, 1901 KILGOUR. Description. Biconvex, both valves elongate Type species. Liitf’iila aurora Hall, 1861 [Late ovoid, with ornament of fine concentric growth Cambrian, North America). lines and regularly disposed coarser growth la- Fig. 5. Wesmnia •’nyapiinnensis: A-B. pedicle valve P91/49: A, exlemal view xl5; B, detail of ornament near lateral margin of valve showing continuous ridges (horizontal) cut by growth lines (vertical) x6(); C, brachial valve P91/52, internal view showing pseudointerarea x 18; I), pedicle valve P91 /5(), internal view showing pseudoinlerarea and pedicle groove (at left) x25; K-(i, pedicle valve P91/51. E. internal view x 15: F .external view x 15: (i. detail ot ornament on midline of valve showing zigzag interference pattern x60. All from AMG 77.4185 KILGOUR. 175 Peter D. Kruse mellae; superimposed asymmetric ridges in two WOOD, P91/61 from AMG 753180 KILGOUR fields concentric about posterior tips of propareas; P91/62 from AMG 190988 LANCEWOOD P91/ fields interface along median area of both valves 63-91/65 from AMG 602162 KILGOUR. as zigzag interference pattern (Fig. 5G). Description. Valves rounded longitudinally Pedicle valve with rounded anterior margin subtriangular in outline. Pedicle valve beak area and near-straight posterolateral margins, latter bears a semicircular to tear-shaped opening subtending apical angle of about 85°. (emarginatura) which breaches posterior valve Pseudointerarea slightly anacline, divided by margin. Valve gently convex in lateral profile, anteriorly expanding pedicle groove. Propareas slightly more strongly rounded posteriorly. Bra¬ divided by flexure lines diverging from beak. chial valve with marginal beak, umbonal region Striations of proparea extend indistinctly across inflated above adjacent lateral flanks; convex in pedicle groove; superimposed straight striations lateral profile, more strongly rounded posteriorly. on groove floor are aligned parallel to valve plane Pedicle valve pseudointerarea divided by of symmetry. Visceral field extremely shallow emarginatura into two discrete anacline, (Fig. 5E). Posterolateral muscle scars elongate, subtriangular propareas, each proparea divided arising beneath propareas. by an anterolateral flexure line into an adnate Brachial valve with prominent orthocline lateral portion and a free portion projecting in¬ pseudointerarea having broad, depressed median ward from shell margin (Fig. 6D). Valve interior segment; margins of depression ill-defined. Low marked by fine radial striae; clearly marked fur¬ median ridge arises from beneath median seg¬ rows of baculate vascula lateralia extend ment (Fig. 5C). anterolaterally from emarginatura; paired elon¬ Remarks. The species is here repre.sented only gate posterior muscle scars lateral to these. Paired by fragments, many of which are internally transversely oriented central mu.scle scars present abraded. As only posterior portions of both valve at about 40% valve length from beak; other interiors are known, the material is assigned to possible paired .scars posterior of these (Fig. 6B). nyapimgensi with question. Brachial valve with apsacline pseudointcrarea The only other known Australian Cambrian closely adnate to inner surface of valve; propareas member of the genus is the coeval IT. cymhricenxis broad, separated by deeply concave diamond¬ Roberts, from the Coonigan Formation of western shaped median plate whose anterior margin is New South Wales, which differs from slightly but clearly elevated above valve "floor. nyapimgemis in having, in the pedicle valve, a Prominent median ridge extends anteriorly to wider pseudointerarea, a deeper pedicle groove about midlength; anterior of this, it trifurcates into and much broader vascula lateralia. and in the a median low ridge, which may extend to near brachial valve, a more acute beak (Roberts and anterior margin, flanked by much shorter and less Jell 1990). distinct lateral ridges. Paired elongate posterior mu.scle scars immediately adjacent to propareas; Family Zhanatellidae Koneva smaller paired central muscle scars located medi¬ ally. astride extension of median ridge, at temii- Genus Kyrshabaktella Koneva, 1986 nations of lateral ridges. Fine radial striae may cover entire valve interior. Type species. Kyrshabaktella certa Koneva, Remarks. The genus is otherwise known only 1986 [Middle Cambrian (Amgan), Kuyandin suite, from Siberia and Kazakhstan. The type species K. Kyrshabakta River, Malyy Karatau, Kazakhstan, certa is distinguished by the raised vi,scera] field USSR]. in some pedicle valves, while in the brachial valve, the median ridge extends almost to the Kyrshabaktella mudedirri Kruse, 1990 anterior margin. (Fig. 6A-G) SEM examination of the shell microstnicture discloses intercalated laminar and columnar lay¬ Kyrshabaktella mudedirri Kruse, 1990: 25, fig. ers beneath a smooth, unpitted external surface 14, pi. 10. (Fig. 6C). Laminar microstructure is characteris¬ Material. Eleven specimens. Pedicle valves tic of the genus, and serves to distinguish it from P91/55 from AMG 984987 KILGOUR. P91/56 the related Late Cambrian genus Dysoristus Bell, from AMG 773185 KILGOUR, P91/57 from which has a pitted external surface and a micro- AMG 094005 LANCEWOOD; brachial valves structure of crosscutting needles (L.E. Popov, P91/58-91/60 from AMG 094005 LANCE¬ pers. comm. 1990). 176 Top Springs Limestone Fig. 6. K\rshahiikrclla mudedinr. A-C, |K-dicle valve P91/5.S from AMG 984987 KILGOUR: A. external view x25; B, internal view x2.S; C. detail of shell microslructurc showing intercalated laminar and columnar layers x2000; D. pedicle valve P91/.S6 from AMG 773185 KILGOUR. internal view showing pseudointerarea, emarginatura (enlarged by shell breakage) and musculature x40; E-F. brachial valve P9I/58 from AMG 094005 LANCEWOOD: E. oblique internal view x25; K. normal internal view x25; (i, brachial valve P9I/59 from AMG 094005 LANCEWOOD. external view x25. Hadrotrcm djagoraii: H. pedicle valve P91/66 from AMG 094(K)5 LANCEWOOD, obliqueextcmal viewshowing pedicle foramen and pseudointcrarea x40; I, pedicle valve P9I/67 from AMG 612119 KILGOUR. internal view x60: J. brachial valve P9I/70 from AMG 094005 LANCEWOOD, external view x40; K-L, brachial valve P91/71 from AMG094(X)5 LANCEWOOD: K, nomial internal view x40: L, oblique inlenial view x40. Order Acrotretida Kuhn (Jenus Hadrotreta Rowell, 1966 Suborder Acrolretidina Kuhn Type species. Acrotreta primaeva Walcott, Superfamily Acrotretacea Schuchert 1902 [Early-Middle Cambrian (upper Bonnia- Family Acrotretidae Schuchert Olenelliis Zone to pre-Alhertella beds), Pioche Subfamily Acrotretinae Schuchert Shale, Pioche, Nevada. USA], 177 Peter D. Kruse Hadrotreta djaeoran Kruse, 1990 Family Acrothelidae Walcott and (Fig. 6H-L) Schuchert Hadrotreta djagoran Kruse, 1990:29, fig. 15, Genus Eothele Rowell, 1980 pl.l 1 [cum syn.]. Material. Eight specimens. Pedicle valves Type species. Acrothele spitrri P91/66 from AMG 094005 LANCE WOOD, Walcott, 1908 [Early Cambrian (Bonnia- P91 /67 from AMG 612119 KILGOUR, P91 /68- Olenellus Zone), Combined Metals Member 91/69 from AMG 094005 LANCEWOOD; of Pioche Shale, Pioche, Nevada, USA). brachial valves P91/70-91/73 from AMG 094005 LANCEWOOD. Eothele napuru Kruse, 1990 Description. Ventribiconvex, valves trans¬ (Fig. 7A-E) versely suboval in outline. Pedicle valve subconical, procline, beak forming highest point Eothelenapurn Kruse. 1990:31, fig. 16, pi. 12. of valve; pseudointerarea a gentle concave Material. Eleven specimens. Pedicle valves flexure of valve, with beak slightly overhang¬ P91/74-91/82 from AMG 612119 KILGOUR, ing subrounded pedicle foramen, divided medi¬ P91/83 from AMG 773185 KILGOUR; brachial ally by narrow inteilrough (Fig. 6H). Growth valves P91/84 from AMG 612119 KILGOUR. lines traverse intertrough generally without in¬ De.scription. Shell subcircular, both valves terruption. Brachial valve low convex: beak low. Apart from bare pseudointerarea (with marginal, inflated above adjacent lateral Hanks growth lines only) astride pedicle foramen, and bounded by gentle but clearly defined fur¬ both valves have ornament of pustulose gran¬ rows extending anterolaterally from apex. ules and concentric growth lines. Pedicle valve interior with low bosslike apical Pedicle valve a low eccentric cone. Lateral process merging gently with valve floor and anterior slopes of apex generally slightly anteriorly and laterally. Internal pedicle open¬ concave in profile; pseudoinierarea procline. ing rounded, flush with surface of apical proc¬ External pedicle foramen slitlike, commencing ess. Cardinal muscle scars subelliptical on as rounded indentation in larval shell margin posterolateral slopes of valve. Baculate vascula and continuing to pre.served margin. Larval lateralia arise near lateral margins of apical shell transversely ovoid, approximate length pits and extend anterolaterally as shallow fur¬ 0.4 mm and width 0.35 mm, with a pair of rows. smoothly rounded knobs anteriorly; a promi¬ Brachial valve interior with short nent hood at posterior margin overhangs pedicle pseudointerarea, medial one-third of which is a foramen. Pedicle valve interior poorly pre¬ sharply defined apsacline median plate; flank¬ served; raised cardinal muscle scars preserved ing propareas approximately orthocline. Me¬ postcrolaterally in some specimens. dian buttress and median ridge are low, colinear Brachial valve gently convex. Larval shell structures separated by a low col; anteriorly, transversely ovoid, approximate length 0.4 mm median buttress flares out as a low platform and width 0.3 mm, bearing a pair of longitudi¬ enclosing a pair of sunken areas, possibly ante¬ nally oriented ridges. At midpoint of each ridge rior muscle scars, straddling median ridge. is a hemispherical dome sumiounted by a knob¬ Cardinal muscle scars subelliptical, each like protuberance. Valve interior with median bounded on its inner margin by raised low septum extending anteriorly from posterior ridge. margin; a broad, low, smoothly rounded, Remarks. Roberts and Jell (1990) have iden¬ anteriorly expanding ridge extends from ante¬ tified an Ordian form from the Coonigan For¬ rior termination of septum. Vascula lateralia mation of western New South Wales as the type extend anterolaterally from posterior valve species H. primaeva. otherwise known Irom margin. Nevada, USA, Compared to H. djagoran, the Remarks. Although pedicle valve internal New South Wales form has a more rounded surfaces are poorly preserved, available frag¬ valve outline, with a clearly different configu¬ ments are sufficient for confident identification as ration of the brachial valve median buttress- E. napuru. Eothele granulata Roberts from the ridge system, wherein the median ridge is much Coonigan Formation of western New South Wales more prominent. is easily distinguished by its much more promi- 178