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 : 237

Phacopidae gen. indet. 2

Figures 12D–F

Material. NMV P312076 (cephalon) from PL1369, Deep Creek, Springfield. Springfield Formation. For locality see fig. 4.

Remarks. This very small cephalon (3 mm in length), and two other small specimens documented below as Phacopidae gen. indet. 3, are the only phacopids known from PL1369. The cephalon undoubtedly belongs to a juvenile individual, and its size is in the range of late meraspides and early holaspides of Acernaspis (cephalic lengths 1.3 mm to 3.3 mm) documented by Ramsköld (1988). It is characterised by a strongly convex glabella that overhangs anteriorly, a short (exsag.) L2, a very large eye occupying almost the entire length of the genal field, a well defined fixigenal lateral border furrow joining the posterior border furrow, and a granulose sculpture. The glabellar convexity, length of L2 and distinct lateral border furrow suggest assignment to Ananaspis , but the last two characters could also be attributed to the small size of the specimen as Ramsköld (1988) observed that in juveniles of Acernaspis L2 is shorter and the lateral border furrow deeper than in adults. The glabella lacks the tuberculation characteristic of Ananaspis , whereas the sculpture is normally relatively coarser in juveniles than adults.

Figures

Figure 12. A, Phacopidella? sp., NMV P1218, dorsal exoskeleton, × 2.7, from PL1393, Keilor. B–C, Struveria sp. 1, NMV P139357, partly disarticulated exoskeleton with hypostome and cephalic doublure exposed, from PL1386, Broadmeadows; B, × 3.4; C, × 4. D–F, Phacopidae gen. indet. 2, NMV P312076, cephalon, × 8, from PL1369, Springfield. (A, E–F are internal moulds).