A Monograph on the Sub-class Cirripedia · Charles Darwin
PLATE 17.
_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.
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