N.B.—Letters of reference the same throughout the Plate.
- A, rostrum.
- B, carina.
- S, moveable scutum, S′, scutum fixed and modified so as to form
part of the shell.
- T, moveable tergum, T′, tergum fixed and modified so as to form
part of the shell.
- In S, and S′,
a is the occludent margin;
b, the basal margin;
m, the plate to which the adductor muscle is fixed;
o, a ledge formed during continued growth, in the upper part of the
fixed scutum, in order to keep the orifice perfectly closed;
this ledge is seen distinctly only in fig. 5.
- In S and S′ the tergal margin is marked by small dashes;
(′) being the upper articular ridge, and
(′′), the second or lower articular ridge: in S′ (′′) is called the
parietal portion of the valve.
- In T and T′, the scutal margin is marked by small dashes;
(′) being the first and upper articular ridge, hardly distinct from the
occludent margin, and called in T′′ the occludent rim;
(′′) is the second or middle, and
(′′′) the lower or third articular ridge, called in T′′ the parietal
portion of the valve;
x is the carinal margin, called in T′ the carinal rim, and
z the basal margin;
o is the occludent margin: in T′, a ledge is formed across the
under side close to the apex, which ledge is necessary to keep
the orifice neatly closed, owing to the apex of the moveable
tergum coming to project freely during growth.
- Fig. 1 a, Verruca Strömia, specimen with the left hand scutum and
tergum fixed and modified into part of the shell.
- 1 b, Verruca Strömia, (with left hand scutum and tergum fixed),
with the valves and compartments separated from each
other; the homologous parts of the opercular valves are
marked by corresponding letters and dashes.
- 1 c, Verruca Strömia, left hand scutum and tergum fixed, viewed
from the under side.
- 1 d, Verruca Strömia, smooth var., reversed specimen, i. e., with
the right hand scutum and tergum fixed and modified into
part of the shell.
- 1 e, Verruca Strömia, shell seen from the under side; the right
hand scutum and tergum (as in 1 d) being the fixed pair:
the moveable scutum and tergum (S, T) are seen in the
shade at the bottom of the shell, and their shape will be
best understood by looking at fig. 1 f. The fixed scutum
and tergum S′, T′, differ a little in shape, and in the form
of their line of junction, from the same two valves (reversed)
in fig. 1 c.
- 1 f, Verruca Strömia, moveable scutum and tergum, seen from the
under side, taken from a specimen, in which (as in
1 d and e) the right hand scutum and tergum were the
fixed pair.
- 2, Verruca Spengleri, scutum seen from the under side,
showing the medial, prominent adductor ridge; taken
from a specimen, in which the right hand scutum and
tergum were fixed.
- 3 a, Verruca lævigata, scutum and tergum, external view of, from
a specimen in which the left hand pair was fixed;
3 b, scutum and tergum, internal view of, from
a specimen, in which the right hand pair was fixed.
- 4, Verruca prisca, scutum and tergum, external view of, from a
specimen, in which left hand pair was fixed.
- 5, Verruca nexa, with the valves separated, the left hand scutum
and tergum being the fixed and modified pair.
- 6, Portion of ribbed shell of a Venus, to which a Verruca
Spengleri had been attached, showing the peculiar form of
the excavation.