AMPHIDESMA. Lam. (from [Greek: Amphô], _ampho_, _ambo_, [Greek: Desmos], _desmos_, _ligamentum_). _Fam._ Mactracea, Lam.--_Descr._ Equivalve, oval or rounded, sub-equilateral, sometimes rather gaping at the sides, with slight posterior fold; hinge with one or two cardinal teeth in each valve, and two elongated lateral teeth, distinct in one valve, nearly obsolete in the other; ligament short, separated from the cartilage, which is elongated and couched obliquely in an excavation of the hinge.--_Obs._ In most bivalve shells, the cartilage and ligament are united in one mass, or placed close to each other; the contrary in this case gives rise to the name, which signifies _double ligament_. This circumstance distinguishes the genus Amphidesma from Tellina, which in other respects it greatly resembles. From Lutraria it may be known by its distinct lateral teeth, and also by its valves being nearly close all round, while the Lutrariæ gape anteriorly. The species do not appear to be numerous, no fossil species are known. A. _Reticulatum_, fig. 85. West India Islands, Brazil, Coast of Pacific, &c. AMPHIPEPLEA. Nilson. The type of this proposed genus is LIMNEA glutinosa, Auct. Gray's edition of Turton, page 243, plate 9. fig. 103. The shell is polished and the inner lip expanded. AMPHISTEGINA. D'Orb. A genus of microscopic Foraminifera. AMPLEXUS. J. Sowerby. A. _Corralloides_, fig. 463. A singularly formed fossil, described as nearly cylindrical, divided into chambers by numerous transverse septa, which embrace each other with reflected margins. It occurs in the Dublin limestone, and resembles a coral or madrepore. AMPLEXUS. A generic name proposed by Captain Brown for HELIX pulchella, Drap. 112, tab. 107-134. Zurama, Leach.