Plio-Pleistocene Peronella 
199 
surface; periproct situated closer to the posterior 
margin and shorter food grooves. 
Teratological specimens of P. ricta are rare, but 
one is known (WAM 83.782) in which ambulacrum 
II is not developed on the aboral surface, hence 
only four petals are present (Figure 4A). On the 
adoral surface, however, ambulacrum II is present, 
the specimen possessing the normal complement 
of five food grooves (Figure 4B). 
Peronella orbicularis (Leske, 1778) 
Figure 5 
Echinodiscus orbicularis Leske, 1778: 208, P1.45, figs 
6,7. 
Peronella orbicularis: Mortensen 1948: 286-291; PI. 
51, figs 1-18 (with full synonymy); McNamara 
1988: 158, figure 12.5. 
non Peronella orbicularis: Foster and Philip 1980:156. 
Material Examined 
WAM 87.610 (157 specimens); WAM 96.210- 
96.218 (nine specimens) from tire Bibra Formation 
(Late Pleistocene), Yaringa Station, Shark Bay, 
Western Australia, from large claypan 400 m west 
of northwest coastal highway; WAM 93.252 (six 
specimens) from the Dampier Formation (Late 
Pleistocene), Peron Peninsula, Shark Bay, from 
southern end of "Big Lagoon", on east side, 1 m 
thick shell bed that is 1 m above high water mark; 
four specimens (WAM 94.266) from a Middle 
Pleistocene unit at Dumbarton, near Busselton in 
the Perth Basin. 
Emended Diagnosis 
Small species of Peronella with circular test with 
thickened rim; relatively broad petals that are 
distally closed and rarely extend more than half 
way to ambitus. Adoral surface of test slightly 
Figure 5 Peronella orbicularis (Leske, 1778) from the Late Pleistocene Dampier Formation, Shark Bay, Western 
Australia: A, H, WAM 93.252c; B, WAM 93.252d; C, WAM 96.211; D, WAM 96.213; E,WAM 96.212; F, 
WAM 96.214; G, WAM 96.210; I, WAM 96.215; J, WAM 96.216; K, WAM 96.217; L, WAM 96.218; all xl.5, 
except G which is x4. 
