_Parietes_: the parietal tubes are remarkably large, and I think this can hardly be an individual peculiarity: the tubes are crossed by many transverse septa, close down to the basis. The _radii_ are narrow, and have jagged, oblique summits: their sutural edges have very distinct septa, barely denticulated, with the interspaces filled up solidly. The _alæ_ have oblique summits; I was unable to make out the structure of their sutural edges. The _Basis_ is very distinctly permeated by pores, which are crossed by transverse septa. The shell and opercular valves of _B. corrugatus_ so closely resemble the same parts in _B. crenatus_, that I should not be much surprised at seeing the two species graduating into each other, if a larger series of specimens, from beds intermediate in age between the Sub-Appennine formations and the present time, were obtained. If indeed the basis of _B. crenatus_ were permeated by pores, the two species could hardly be discriminated. _Section_ D. _Parietes permeated by pores. Basis and Radii not permeated by pores._ 25. BALANUS PORCATUS. Pl. 6, fig. 4 _a_-4 _e_. BALANUS PORCATUS. _Emanuel da Costa._ Hist. Nat. Test. Brit., p. 249 (1778). LEPAS BALANUS. _Linn._ Syst. Naturæ (1767). ---- ---- _Born._ Testacea Mus. Cæs. Desc., Tab. 1, fig. 4, (1780). ---- ---- _Chemnitz._ Syst. Conch., 8 Band., Tab. 97, fig. 820, (1785). BALANUS ARCTICA PATELLIFORMIS. _Ellis._ Philosoph. Transact., vol. 50, Tab. 34, fig. 18 (1758). ---- SULCATUS. _Bruguière._ Encyclop. Method., Tab. 164, fig. 1 (1789). LEPAS COSTATA and BALANUS. _Donovan._ British Shells, 1802-1804, Tab. 30, fig. 1, 2. LEPAS SCOTICA. _W. Wood._ General Conchology, Pl. 6, fig. 3, sed non _Lepas balanus_, Pl. 7, fig. 3, (1815). BALANUS ANGULOSUS. _Lamarck_ (1818), in _Chenu_, Illust. Conch., Tab. 11, fig. 11. ---- TESSELATUS. _Sowerby_ (!). Mineral Conchology, Tab. 84 (1818). ---- SCOTICUS. _Brown._ Illust. Conch. Great Britain, Pl. 7, fig. 2, sed non, Pl. 6, fig. 9 et 10 (1827); 2d edit., Pl. 53, fig. 1-3, 22, 23 et Pl. 54, fig. 1-3. ---- GENICULATUS. _Conrad._ Journal Acad. Philadelphia, vol. 6, part 2, p. 265 (1830), Tab. 11, fig. 16. ---- ---- _Aug. Gould_ (!). Report on the Invertebrata of Massachussetts, fig. 9 (1841). _Shell white, generally sharply ribbed longitudinally: radii with their summits almost parallel to the basis. Scutum longitudinally striated: tergum with the apex produced and purple._ _Var._ (_a_): _Walls without longitudinal ribs_. Mus. Brit., Cuming, Stutchbury, Jeffreys. _Hab._--South shores of England, Ireland, Scotland, Shetland Islands, Iceland, Davis's Straits, 66° 30′ N.; Lancaster Sound, 74° 48′ N. (Mr. Sutherland). Maine and Massachussetts, United States. China (?). In deep water, common on shells, crustacea, and rocks, sometimes imbedded in sponges.