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 U], [Creusia spinulosa], var. 11, shell seen from above; [6 u], scutum and tergum, calcified together, external view.
Fig. [1 a], [Chelonobia testudinaria], shell seen from above; a specimen
has been chosen, with some of the radii smooth, and others
more or less notched; [1 b], scutum, internal view of; [1 c], tergum, internal view of; [1 d], scutum and tergum, joined together, external view of.
[4], Carina of [Chelonobia patula], seen from within; a a, outer lamina of wall, joined by the longitudinal septa to b, the inner lamina; e c e, sheath, descending to the base of shell, with the middle part largely hollowed out; the
upper part of the sheath, above d d, is transversely marked by the lines of attachment of the opercular membrane; d, d, alæ.
b, thick outer lamina of the radius, transversely pitted; beneath
this pitted portion, which forms only the outer surface of the radius, and distinct from the
inner portion a, the arborescent and dentated sutural edges of this outer lamina are seen.
c, outer lamina of wall of compartment.
d, the exterior septum, connecting the outer lamina of the wall to the inner lamina;
the basal edge of the inner lamina of the wall is seen beneath and without the lower
end of the inner portion (a) of the radius.
B A B, Compound rostrum: A being the true rostrum.
B B, the rostro-lateral compartments, which normally, in the [Balaninæ], are quite confounded
with the true rostrum: the sutures separating these three compartments are not continued through the
outer lamina.
C, left-hand lateral compartment.
D, left-hand carino-lateral compartment.
E, carina.
S S, Sutures, six in number, separating the six compartments.
a, outer lamina of wall of compartment, whence the radiating, longitudinal septa (left unshaded)
arise, and at the opposite end blend into the indistinct inner lamina, viz. b, (see
fig. 4, in last plate.)
c′, sheath.
d, ala, forming, as usual, part of the sheath.
e, inner portion of the radius.
f, f, outer lamina of the radius (see b, in fig. 5, in last plate), of great
thickness, and externally deeply pitted;—the sharp ridges between the pits, produce in the
section the points, such as that marked by the outer f.
[2 a],””section of one of the transverse circumferential loops, formed by the folded wall of a compartment. The wall itself is formed of an outer and inner lamina, with longitudinal septa. The internal surfaces of the loop-part are connected by special shelly plates or longitudinal septa.
[2 b],””scutum and tergum united together by the opercular membrane (with horny ridges), seen from the inner side.
[3], [Coronula diadema], shell, seen from the outside; [3 a], scutum and tergum joined together by the opercular membrane, seen from the outside; [3 b], scutum cleaned and enlarged, seen from the inside.