_Genera_--PLATYLEPAS, TUBICINELLA, AND XENOBALANUS.
Fig. 1 _a_, Platylepas bissexlobata, shell of, viewed from the
under side; A, rostrum; B, lateral compartment; C,
carino-lateral compartment; E, carina. These letters are
placed opposite the inward folds of each compartment
forming the midribs.
1 _b_, Platylepas bissexlobata, shell of, viewed externally.
1 _c_, " " scutum and tergum, viewed
externally and separated.
1 _d_, " " lateral compartment, viewed
from the inside, showing the
inward folded wall or midrib;
_a′_, ala; _d_, radius.
2 _a_, Platylepas decorata, shell, viewed externally; A,
rostrum; B, lateral compartment; C,
carino-lateral compartment; E,
carina. These letters are placed
opposite the inward folds of each
compartment.
2 _b_, " " minute portion of external
surface of wall, magnified.
3 _a_, Tubicinella trachealis, natural size; _p_, tubular
soft lip leading into sack; _s_, scutum; _t_, tergum.
3 _b_, Tubicinella trachealis, carino-lateral compartment of
a young specimen, natural size; _e_, broken summit of wall;
_d_, radius: the dotted lines, connecting the two figures,
show the size and form which this compartment would have
attained, if it could have grown without the summit
constantly breaking away.
3 _c_, Tubicinella trachealis, scutum and tergum viewed from
within, and connected by layers of thickened membrane; the
scutum is to the left-hand.
4 _a_, Xenobalanus globicipitis, enlarged; _b_, skin of the
porpoise, with the shell imbedded; at _c_ the lower end of
the prosoma of the included animal's body is supposed to be
seen through.
4 _b_, Xenobalanus globicipitis, shell greatly enlarged, seen
from above, with the basal membrane at the bottom; the
peduncle-formed body having been removed.
A, rostrum, on the inner side of this and the adjoining
compartments, the transversely ribbed sheath can be seen.
B, lateral compartment.
C, carino-lateral compartment.
E, carina; these compartments are separated by the sutures
_s s_, which run from the top of the shell to the bottom,
along the ends of the six rays formed by the adjoining
portions of the inwardly folded compartments.
_a_, alæ, of rectangular shape.
_d_, pseudo, or complimentary radii.
4 _c_, Xenobalanus globicipitis, small portion of external
surface of wall of shell, showing the external lamina,
_a a_, which consists only of narrow ledges (expanding
and contracting) on each side of the longitudinal septa,
_c_; _b_, the internal lamina.