_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.