_Genera_--CHELONOBIA AND CORONULA.
Fig. 1, Transverse section of shell of Chelonobia testudinaria.
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, Coronula balænaris, shell seen from above.
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.
4, Section, in a vertical plane, through the skin of a whale,
on which a _Coronula diadema_ had been attached, but has
been wholly removed: the two curved, horn-like projections
occupied two of the eighteen cavities on the under side of
the shell, formed by the folded walls: the blacker part is
the epidermis; the lighter part is the yellowish fibrous
tissue of the skin under the epidermis.
5, Coronula reginæ, shell seen from the outside.
6, Coronula barbara, internal view of the basal margin and
inside of one of the compartments, exhibiting the
circumferential transversely looped ends of the folds of
the wall, with the inner surface transversely wrinkled.
7-9, diagrams, showing how one of the circumferential transverse
loops of the wall becomes divided into two transverse
loops, thus giving rise to another fold in the wall.
10, diagrams, showing how the wall of the young shell in
Coronula, from being (_a_) simply sinuous, becomes deeply
folded (_b_); the folds lastly (_c_) expanding transversely
at their ends, thus giving rise to the circumferential
transverse loops, as in fig. 7.