Cairns—New flabellid genus from Australian Cenozoic
415
Figure 4. Juvenile specimen of Periplacotrochus, similar to that described as P. elegans, USNM 67999, Muddy Creek, Victoria, middle Miocene: (1) lateral view of specimen showing characteristic broad attachment to a shell fragment; (2) stereo view of calice showing 32 septa. Scale bars =1mm.
Diagnosis.—Septa arranged in three size classes, but with 27–32 primary septa, resulting in 104–128 septa.
Occurrence.—Janjukian (late Oligocene): Torquay and Spring Creek (near Geelong), Victoria, Australia.
Description.—The corallum has a bimodal edge angle, the lower thecal edges making an angle of 91º–98º (Fig. 3.9, 3.13), whereas the upper thecal edges diverge at only 34º–46º; the lower thecal edges are acute and bear a low crest, whereas the upper thecal edges are less acute and rounded near the calice. The thecal faces are planar to slightly convex, making a face angle of 36º–45º (Fig. 3.10, 3.14). The largest corallum (the holotype) is 37 × 26mm in calicular diameter and 33mm in height. The calice is elliptical, the GCD:LCD ranging from 1.36 to 1.66; the H:GCD ranges from 0.89 to 1.21. The pedicel is small (1.8–2.0 × 0.75–1.05 mm), the greater axis aligned with the GCD. The septa are arranged in three size classes, the holotype
having septa arranged as 28:28:56 (112 septa), but other coralla have 27–32 primaries and a total of 104–128 septa. The primary septa are slightly exsert and have slightly sinuous axial edges, the lowermost edges fusing to the lamellar columella. The secondaries are about half the width of the primaries and do not attain the columella. The tertiaries are small to rudimentary but consistently present over aGCDof about 30mm. The fossa is of moderate depth and contains a prominent lamellar columella, usually consisting of a single, thick (0.5mm) lamella (Fig. 3.12), but sometimes as two or three aligned lamellae (Fig. 3.15, 3.16).
Materials.—Torquay (near Geelong), Victoria, Janjukian (late Oligocene), two coralla, USNM 67954. Spring Creek (also known as Bird Rock Cliffs), Janjukian (late Oligocene), four coralla, USNM 67952.
Remarks.—Periplacotrochus magnus is compared to the clo- sely related P. deltoideus in the account of the latter species.
Periplacotrochus elegans Tenison-Woods, 1878a, nomen dubium
1878a Placotrochus elegans Tenison-Woods, p. 189, pl. 1, fig. 1, 1a.
1927 Placotrochus elegans; Felix, p. 417. 1971 Placotrochus elegans; Fletcher, p. 32. 1989b Placotrochus elegans; Cairns, p. 75.
Types.—Holotype deposited at the Australian Museum (F.1697) (Fletcher, 1971). Type locality: Muddy Creek, Victoria, Balcombian (middle Miocene).
Diagnosis.—The species cannot be diagnosed as it is probably a juvenile stage of another species.
Occurrence.—Known only from the type locality.
Description.—The holotype is only 3mm tall, with a com- pressed calice (3.0 × 1.5mm in diameter, GCD:LCD = 2; H: GCD = 1) and an elongate basal attachment (1.65mm in greater diameter). The edge angle is about 21º. According to
Figure 3. (1–4) Periplacotrochus inflectus: (1, 2, 4) NMV P27107, syntype, lateral, edge, and calicular views, respectively; (3) calicular view of specimen NMV P134078. (5–8) P. cudmorei, holotype, USNM 1283876, lateral, edge, calicular, and oblique calicular views, respectively. (9–16) P. magnus: (9–11) holotype, NMV P27114, lateral, edge, and calicular views, respectively; (12) USNM 67954, damaged specimen showing its lamellar columella; (13–16) USNM 67954, lateral, edge, calicular, and oblique calicular views of same specimen, respectively. (1, 2, 5–16) Scale bars = 10mm; (3, 4) scale bars = 5mm.
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