_Genera_--PYRGOMA AND CREUSIA.
Fig. 1 _a_, Pyrgoma grande; 1 _b_, scutum and tergum, calcified
together, external view of; 1 _c_, scutum and tergum,
internal view of; 1 _d_, the two scuta and terga, external
view, seen from above, having their natural position, when
closed.
2 _a_, Pyrgoma milleporæ, shell viewed from above; 2 _b_,
internal view of, showing the sheath; 2 _c_, scutum and
tergum, united, external view of; 2 _d_, scutum, _var._
external view of; 2 _e_, scutum, internal view of; 2 _f_,
tergum, internal view of.
3 _a_, Pyrgoma dentatum shell, external view of; 3 _b_,
scutum, _var._ 1, external view of; 3 _c_, tergum, _var._
1, external view of; 3 _d_, tergum, _var._ 2, external
view of; 3 _e_, scutum, _var._ 3, external view of; 3 _f_,
tergum, _var._ 3, external view of; 3 _g_, scutum and
tergum, _var._ 1, joined together, internal view of.
4 _a_, Pyrgoma crenatum, scutum, external view of, showing
the great depending adductor plate and large occludent
ledge; 4 _b_, external view of.
5 _a_, Pyrgoma monticulariæ, external view of; 5 _b_, another
specimen, internal view of; 5 _c_, another specimen,
external view of; 5 _d_, portion of circumference of shell,
viewed externally, much magnified, showing the outer
lamina, and the irregular, longitudinal septa; 5 _e_,
another specimen of the same, with the longitudinal septa
more regular; 5 _f_, scutum and tergum completely calcified
together, external view of.
6 _a_, Creusia spinulosa, shell, seen from above.
6 _b_, 6 _c_, Creusia spinulosa, _var._ 1, scutum and tergum,
internal view of; 6 _d_, scutum and tergum, joined
together, external view of.
6 _e_, 6 _f_, 6 _g_, Creusia spinulosa, _var._ 2, 6 _e_,
scutum, internal view; 6 _f_, tergum, internal view of;
6 _g_, tergum, of another specimen, internal view of.
6 _h_, Creusia spinulosa, _var._ 3, scutum and tergum joined
together, external view of.