two directions by _Lithotrya
dorsalis_, with the calcareous basal discs in the upper
cavity, serving as a bridge for crossing an old cavity.
About twice natural size.

1_a'._ _Lithotrya dorsalis_, (nearly twice nat. size), with the
basal calcareous cup adherent; (_a_), rostrum on same scale,
seen externally.

1_b'._ _Lithotrya dorsalis_, rostrum and the rostral corners of
the two scuta, together with a small portion of the
subjacent membrane of the peduncle, with its calcareous
scales; viewed externally, greatly magnified, showing the
inferior crenated edges of the scales.

1_c'._ _Lithotrya dorsalis_, basal calcareous cup, one and a half
the natural size; this is the largest specimen which I have
seen.

2. _Lithotrya Nicobarica_, (magnified nearly twice;) attached to
the rock, copied from Reinhardt; (_a_), rostrum on the same
scale, with the other valves, seen externally; (_b_),
section of the row of discs; (_c_), extreme point of the
peduncle, extending beneath the row of discs.

2_a'._ Rock bored by _Lithotrya Nicobarica_, showing the row of
calcareous discs, copied from Reinhardt.

3. _Lithotrya cauta_, magnified between seven and eight times;
(_a_), scutum; (_b_), tergum.

3_c._ _Lithotrya cauta_, latus, greatly magnified.

3_d._ _Lithotrya cauta_, uppermost scales of the peduncle, greatly
magnified.

3_e._ _Lithotrya cauta_, star-shaped discs of hard chitine,
supported on a peduncle of the same substance, taken from
the lower exterior surface of the peduncle, very greatly
magnified.

4. _Lithotrya Rhodiopus_, (magnified five times,) internal views
of; (_a_), scutum; (_b_), tergum; (_c_), latus; (_d_),
carina.

5. _Lithotrya Valentiana_, (magnified between three and four
times;) (_a_), internal view of scutum and tergum, locked
together; (_b_), capitulum seen from vertically above;
(_c_), internal view of carina; (_d_), section across the
middle of the carina.

TAB. IX.

Fig.

1. _Lithotrya truncata_, (magnified four times.)

1_a'._ _Lithotrya truncata_, capitulum seen from vertically above,
not so distinctly represented as in fig. 5 _b_, Pl. VIII.

1_b'._ _Lithotrya truncata_, internal views of valves; (_a_),
rostrum, with a few sub