Phacopidae, Hawle and Corda, 1847

Sandford, Andrew C. & Holloway, David J., 2006, Early Silurian phacopide trilobites from central Victoria, Australia, Memoirs of Museum Victoria 63 (2), pp. 215-255 : 235-237

Phacopidae gen. indet. 1

Figures 6L–M

Lochkovella ?.— Rickards and Sandford, 1998: 753.

Material. NMV P136136 (cephalon) from PL 1638, Williams locality W25, Strathewen. Yan Yean Formation. The locality occurs in strata mapped just below the boundary of the Anderson Creek Formation and the Dargile Formation ( Garratt, 1972). Strata mapped at this horizon in some areas around Melbourne were reassigned by Rickards and Sandford (1998) to the Yan Yean Formation. The presence of a distinctive encrinurid at PL 1638 that otherwise occurs in the upper beds of the Yan Yean Formation at Heathcote (at PL 2259, Thomas locality F41, Parish of Heathcote) and at Upper Plenty ( PL 1697, PL 1699) supports the assignment of strata at PL 1638 to the Yan Yean Formation. For localities see Thomas (1940), Williams (1964) (fig. 2) and Sandford (2006) (figs 2, 4).

Description. Cephalon semi-elliptical in outline, sagittal length about 60% maximum width. Glabella gently to moderately convex (sag., tr.), frontal lobe low, width across frontal lobe approximately twice width across L1 and a little more than sagittal length. Axial furrow wide and very deep, diverging at about 60° in front of S1. Occipital ring comprising 40% maximum cephalic width, raised high medially, shorter (exsag.) and obliquely directed laterally but without well defined lateral lobes. Occipital furrow deep. L1 of almost uniform length (sag., exsag.) across glabella, high medially, inner edge of lateral node obscured. S1 very deep and wide laterally, directed slightly forward of transverse, shallowing abruptly close to sagittal line. S2 deep, weakly convex forward, its outer end opposite posterior edge of eye, running parallel to S1 and very close to it. S3 not clear but posterior branch apparently directed posteromedially at about 30° to transverse and with inner end more or less level with glabellar midlength (sag.) and close to S2. Eye small and obliquely oriented, situated almost its own length(exsag.)fromposteriorborderfurrowandwithmidlength opposite glabellar midlength (sag.). Palpebral furrow moderately impressed, weakly arcuate, continuous with postocular furrow that is of similar depth and reaches lateral border furrow. Palpebral lobe not raised above palpebral area. Visual surface not well preserved but appears greatly reduced, ovate in outline with lower edge distant from lateral border furrow, and with about 10 lenses. Posterior border furrow deep adaxially, continuous with wide, deep lateral border furrow. Posterior border uniformly short (exsag.) except distally. Genal angle rounded. Lateral border weakly convex, wider behind intersection of postocular furrow than in front. Sculpture obscured by preservational pitting covering most of cephalic surface.

Remarks. Tentativeassignmentofthisspecimento Lochkovella by Rickards and Sandford (1998) was based on the small and forwardly placed eye, the deep and continuous posterior and lateral cephalic border furrows, the deep postocular furrow, and the apparent absence of coarse tuberculation on the glabella. These characters as well as the narrow cheeks invite comparison with the Czech Early Devonian (Pragian) species ʻ Phacops ( Phacops ?)ʼ hanusi Chlupáč, 1977 and ʻ P. (P.?)ʼ veles Chlupáč, 1972, which were assigned to Lochkovella by Sandford (2004). However, other characters of the specimen are incompatible with assignment to Lochkovella . Such characters include the glabella of low convexity that does not overhang anteriorly, and the very small, elliptical visual surface of the eye with its lower edge distant from the lateral border furrow. It is possible that the specimen belongs to an undescribed genus.

The monotypic Orygmatos Sandford, 2000 , from a slightly higher stratigraphic horizon low in the Melbourne Formation at Yan Yean, 10 km to the north-east, also has very small eyes with an elliptical visual surface. Compared with the present specimen from Strathewen, Orygmatos has an occipital ring that is more expanded (sag., exsag.) and prominent medially, L1 is very short (sag., exsag.) and markedly depressed, the composite glabellar lobe expands more strongly forward and is coarsely tuberculate, the palpebral furrow meets the postocular furrow in an broad curve rather than an abrupt angle, and the posterior border furrow and fixigenal portion of the lateral border furrow are very wide. Denckmannites Wedekind, 1914 has even more greatly reduced eyes than the Strathewen specimen, much weaker palpebral and postocular furrows, a more elongated glabella, wider cheeks, and a longer anterior border. The small-eyed Denckmannites rutherfordi Sherwin, 1968 from the Ludlow–Přídolí of central western New South Wales was assigned to Lochkovella by Chlupáč (1977) but Sandford (2004) noted that the presence of strong notching in the lateral part of the vincular furrow excluded the species from that genus, a conclusion supported by the apparent absence of granular sculpture on the exoskeleton. The very low cephalic profile (sag., tr.), the more pentagonal outline of the glabella, the subparallel alignment of S2 and S3, and the broadly arcuate union of the palpebral and postocular furrows distinguish rutherfordi from the Strathewen specimen.

Figures

Figure 6. A–H, I?, J–K, Ananaspis kenleyi sp. nov. A, holotype NMV P136802, pygidium, × 6, from ʻBroadhursts Creekʼ, Wandong. B–C, paratype NMV P136821, cephalon × 4, from PL375, Kilmore East. D, paratype NMV P140156, cephalon, × 4.5, from PL375, Kilmore East. E, paratype NMV P140403, cephalon (fragment), × 2.5, from PL1691, Kilmore East. F, paratype NMV P137165, cephalon, × 3.5, from PL286, Wandong. G, paratype NMV P140154, thoracopygon with pygidium displaced and inverted, view of pygidium, × 4.5. H, paratype NMV P136820, pygidium with circular textural markings, × 4, from PL375, Kilmore East. I, paratype NMV P136815 cephalon, × 3, PL377, Kilmore East. J, paratype NMV P136819, exoskeleton with displaced cephalon, view of doublure,× 4, PL375, Kilmore East.K, paratype NMV P138648, thoracopygon, × 2.5, from ʻBroadhursts Creekʼ, Wandong. L–M, Phacopidae gen. indet. 1, NMV P136136 cephalon, × 5, from PL1368, Strathewen. (B–C, F–G, I–K are internal moulds).