Ananaspis sp. 2

Sandford, Andrew C. & Holloway, David J., 2006, Early Silurian phacopide trilobites from central Victoria, Australia, Memoirs of Museum Victoria 63 (2), pp. 215-255 : 232

Ananaspis sp. 2

Figures 10B–C

Material. NMV P136142 (cephalothorax) from PL1371, about 50 m SW of corner of Murray Road and Elizabeth Street, Coburg. Dargile Group, precise stratigraphic horizon uncertain.

Description. Glabella wide, maximum width 110% sagittal length and 65% maximum cephalic width, overhanging anterior border. Axial furrow very shallow and slightly convergent forwards adjacent to occipital ring, very deep adjacent to composite lobe, straight and diverging forwards at about 65°. Occipital ring 50% maximum glabellar width, medial section raised, separated from short (exsag.) lateral section by deep notch in anterior margin. Occipital furrow transverse medially, deep. L1 short (exsag.) 13% sagittal cephalic length, lateral node low, globular, isolated from remainder of L1. S1 deep laterally, shallower medially where it forms posterior edge of a slightly depressed triangular area between L1 and composite lobe. Length of L2 16% sagittal cephalic length. S2 and posterior branch of S3 of moderate depth, wide, uniformly arcuate, almost reaching axial furrow. S2 directed obliquely inwards-forwards at about 15° to transverse. Posterior branch of S3 oriented transversely opposite glabellar midlength (sag.), anterior branch directed parallel to axial furrow. Posterior border furrow deep and wide (exsag.), widening abaxially, continuous with wide and deep lateral border furrow on fixigena. Postocular area 14% sagittal cephalic length. Glabellar tubercles large to very large, low and flat-topped, distributed irregularly with moderate density. Tuberculation subdued on genal field.

Remarks. The formation to which the strata at PL1371 belong is difficult to determine as the site is no longer exposed. Fossils are uninformative in this respect as the trilobite is the only fossil known and is not known from elsewhere.

The glabellar tuberculation, depth and placement of the lateral glabellar furrows, depth of the posterior and lateral cephalic border furrows and length of the postocular area are comparable to Eastern European and Central Asian species of Ananaspis . In the greater width of the glabella the Coburg species is closest to A. crossleii from the Yass district of New South Wales (maximum glabellar width 60% maximum cephalic width; see Sherwin, 1971, pl. 2, figs 6–9, pl. 3, figs 1–7). The Coburg specimen differs from crossleii in having a wider glabella with larger, flat and less densely distributed tubercles, and a longer (exsag.) postocular area (postocular length 14% sagittal cephalic length versus 10% in crossleii ).

Figures

Figure 10. A, D, I, Ananaspis sp. 1 from PL1338, Wallan. A, D, NMV P139354, cranidium, × 6.5. I, NMV P139356 cephalon (fragment), enlargement of eye, × 9. B–C, Ananaspis sp. 2, NMV P136142, damaged cephalothorax, from PL1371, Coburg; B, × 1.4; C, × 1.2. E–G, J, Ananaspis typhlagogus? (Öpik, 1953), NMV P147055, cephalon (crushed) from PL206, Wallan; E–G, × 3; J, × 2.5. H, Ivops wallanensis gen. et sp. nov., paratype NMV P139326, thoracopygon, × 3, from PL206, Wallan. K, Phacopidae gen. indet. 3, NMV P312077, partly disarticulated thoracopygon, × 4.5, from PL1369, Springfield. (A, C, E–H, J–K are internal moulds).