—————— cheloniæ (!) Ib. Ib.
Anatifa tricolor (?). Quoy et Gaimard. Ann. des Sc. Nat., 1st series, tom. x, 1827, Pl. vii, fig. 7, et Voyage de l’Astrolabe, Pl. xciii, fig. 4.
———— substriata (!). Conrad. Journal Acad. Nat. Sc., Philadelphia, vol. vii, 1837, p. 262, Pl. xx, fig. 14.
L. valvis lævibus; scutorum dentibus internis umbonalibus nullis; carinâ à cæteris valvis, furcâ etiam a scutorum basali margine, paululum distante; pedunculi parte superiore aut pallidâ aut aurantiacâ.
Valves smooth; scuta destitute of internal umbonal teeth; carina standing a little separate from the other valves, with the fork not close to the basal margin of the scuta; uppermost part of peduncle either pale or orange-coloured.
Extremely common; attached to ships’ bottoms, from all parts of the world; on floating timber; associated with L. anatifera and L. anserifera. Mediterranean. Attached to turtles, in the Atlantic, lat. 30° north. West Indies. Falkland Islands. “South Seas,” collected by A. Menzies. Port Stephen, Australia.
General Appearance.—Capitulum laterally flat; length varies in proportion to the breadth; valves white, somewhat translucent, moderately thick, very smooth, but with faint traces of radiating lines; in some varieties, surface rather irregular along the zones of growth. Scuta without any internal teeth, and with scarcely any trace of the internal basal rim; upper angle little acuminated; the occludent margins of the two scuta stand rather separate from each other, showing a wide space of corium between them: these margins are arched and protuberant, but with the lower part a little hollowed out; basal margin a little curved. In one specimen alone, I saw a trace of a diagonal line of square coloured marks, like those common in L. anatifera. Terga rather broad, with the basal angle not much acuminated. The degree of prominence and outline of the double occludent margin varies very much. Carina, separated by a rather wide space from the scuta and terga; of very varying shape, the upper part not much acuminated, generally very flat, sometimes exteriorly marked by a central depressed line; never barbed; occasionally, (in a specimen from Australia,) middle part so wide as almost to become spoon-shaped; on the other hand occasionally of nearly the same width throughout; somewhat constricted above the fork. Fork deeply embedded as usual; situated, in fresh specimens, a little way beneath the basal margins of the scuta, instead of touching them, as in the other species; forks of varying width, not so abruptly inflected as in many species; sometimes much narrower than the upper widest part of the valve, sometimes nearly twice as wide; prongs of fork not very sharp, diverging at about a right angle, with the rim between them reflexed. The apex of the carina extends up between the terga for barely half their length, instead of up fully three fourths of their length, as in L. anatifera.
The chitine membrane at the base of the capitulum, especially at the anterior and posterior ends, is covered with beautiful, little, embedded, yellowish beads, about 3/2000th of an inch in diameter; above this, on each side of the carina, there is a space with similar but smaller little spheres, and still higher up still minuter ones; others occur on different parts of the capitulum; these spaces are seen to be distinctly separated from each other, and present a beautiful appearance under a high power.
Peduncle, as long as, or rather longer than, the capitulum: in one set of specimens, however, it was thrice or four times as long as the capitulum. The peduncle, in some specimens, was conspicuously covered with transverse plates of yellowish hard chitine.