198 
K.J. McNamara 
Description 
Test moderately large, reaching up to 86 mm test 
length (TL); ovate, with a broadly rounded 
ambitus; posterior sometimes broadly acuminate; 
highest at mid test length at apical system; height 
15-23%TL; juveniles almost flat; at margin test 
height varies between 8-20%, being higher in small 
individuals; test longer than wide, width ranging 
between 78-94%TL; widest in small individuals 
(Figure 3G,H), narrowing with increase in test size. 
Aboral surface rises gently from lateral margin, 
increasing angle of slope up to apex. Apical system 
slightly anterior of centre; tuberculate, with four 
gonopores. Petals closed or almost closed distally. 
Increase in relative length during ontogeny. Paired 
petals of equal length (18-28%TL), but slightly 
shorter than anterior petal in ambulacrum III (23- 
34%TL); extend just over half way to the ambitus 
(Figure 3B,C,E); petals narrow, with maximum 
width varying between 7-15%TL; relatively broad 
in juveniles (Figure 3G), narrowing relatively 
during ontogeny; petals widest at about mid-petal 
length. Interporiferous region 4-8%TL, being 
widest in smallest specimens. Inner pores of each 
pair circular; outer pore elongate; connected by 
shallow interporiferous furrow. 
Adoral surface flat, sloping at very low angle to 
slightly sunken peristome. Peristome circular and 
surrounded by weakly developed bourrelets 
(Figure 3D); central or slightly anterior of centre. 
Food grooves short, but relatively deeply sunken 
close to peristome (Figure 4B). Periproct circular to 
transversely oval; similar in size to peristome and 
situated less than twice its diameter from the 
posterior border (4-ll%TL). 
Discussion 
Peronella ricta can be distinguished from the 
living P. lesueuri in a number of ways. Although 
being a relatively large species of Peronella, P. ricta 
does not attain as large a test size. The test of P. 
ricta is much thicker, P. lesueuri being a particularly 
thin species of Peronella. At comparable test sizes, 
the petals of P. ricta are longer. Furthermore, they 
are virtually closed distally, whereas those of P. 
lesueuri are open. The interporiferous zone of the 
petals in P. lesueuri is slightly more swollen than in 
P. ricta. On the adoral surface, the food grooves are 
much deeper close to the peristome in P. ricta, 
resulting in the presence of more pronounced 
bourrelets. 
The other species of Peronella that occurs in the 
Shark Bay region today, and did so in the Late 
Pleistocene, is P. orbicularis. P. ricta can be 
distinguished by its larger size; relatively narrower 
test that is more rounded posteriorly; more evenly 
sloping aboral surface; relatively longer, narrower 
petals; flatter adoral surface; periproct set closer to 
the posterior ambitus, less than two periproct 
Figure 4 Peronella ricta (Gregory, 1892) from the 
Middle Pleistocene Gladstone Member of the 
Carbla Oolite, near Gladstone Jetty, Shark 
Bay, Western Australia: WAM 83.782, A, 
aboral view of teratological specimen with 
only four petals; B, adoral view of same 
specimen; both x 1.5. 
diameter widths away, whereas in P. orbicularis it 
is at least two periproct widths away. The test of P. 
ricta is relatively narrower than that of the third 
living Western Australian species, P. tuberculata. 
Furthermore, it has narrower petals; flatter adoral 
