_Parietes_, the longitudinal septa sometimes stand near each other, making the parietal pores small. The _radii_ have oblique summits, but to a variable degree; their septa are unusually fine, and are denticulated on their lower sides; the interspaces are filled up solidly. The _alæ_ have their summits very oblique, with their sutural edges nearly or quite smooth. In most of the fossil specimens, and slightly in some of the recent specimens, the surface of the sheath presents an unusual character, in a narrow, longitudinal, slightly raised border, running along the sutures, on the carinal side of each compartment. _Basis_ thin, porose; sometimes with an underlaying cancellated layer. _Mouth_: labrum with six teeth: mandibles with the fourth and fifth teeth small, either sharp, or blunt: maxillæ with a straight edge, or with the inferior part slightly prominent. _Cirri_ with the rami of the first pair unequal by four or five segments: the segments in the shorter ramus are extremely protuberant. The segments in the second cirrus only moderately protuberant: but all the specimens were in bad condition, and it appeared as if, in the Panama specimens, the segments of the second cirrus were more protuberant than in the Philippine Island specimens. In the posterior cirri there are from three to five pairs of spines on each segment: even amongst the Panama specimens some had three and some four pairs, and a white Panama specimen had five pairs of spines. All the recent specimens which I have seen, were, with one exception, attached to various shells and crabs, and to each other. The Peruvian specimen was associated with _B. flosculus_. The tertiary specimens are often congregated together into great masses. Including the recent and fossil specimens, this species encircles the globe. During the miocene period it seems to have been the commonest existing sessile cirripede; now, it does not appear to be common, excepting, perhaps, at Panama: Mr. Cuming procured only one specimen from the Philippine archipelago. 19. BALANUS AMPHITRITE. Pl. 5, fig. 2 _a_-2 _o_. LEPAS RADIATA. _Wood's_ General Conchology (1815), Pl. 7, fig. 7. ---- MINOR? _Wood's_ General Conchology (1815), Pl. 7, fig. 6. ---- BALANOIDES. _Poli._ Testacea utriusque Siciliæ (1795), Tab. 5. BALANUS BALANOIDES. _Risso._ Hist. Nat. de l'Europe Merid., tom. iv, 1826. _Shell longitudinally striped with purple or pink; sometimes with the stripes confluent; sometimes wholly white. Scutum internally with a prominent broad adductor ridge._