PLATE 9.
Sub-Genus—ACASTA.

• Fig. 1 a, Acasta spongites; 1 b, scutum, external view; 1 c, scutum, internal; 1 d, tergum, internal.
• 2 a, Acasta sulcata; 2 b, var., lateral compartment of; 2 c and 2 d, terga, internal views of two varieties.
• 3 a, Acasta cyathus; 3 b and 3 c, scutum and tergum, internal views.
• 4, Acasta undulata, scutum, external view.
• 5 a, Acasta glans, basis seen from within; 5 b, compartments of a smaller specimen, seen from within; carina on the right-hand, cut into two; carino-lateral and lateral compartments to the left-hand; 5 c, tergum, internal view.

• 6 a, Acasta lævigata, tergum, internal view; 6 b, another var.
• 7 a, Acasta fenestrata; 7 b, scutum, and 7 c, tergum, internal views.
• 8 a, Acasta purpurata; 8 b, scutum; 8 c, tergum, internal views.
• 9 a, Acasta sporillus; 9 b, carino-lateral compartment (almost rudimentary) and lateral compartment, seen from within; 9 c and 9 d, scutum and tergum, seen from within.