leather-cup: A genus of the order of algae, belonging to the cryptogamia class of plants; and in the natural method ranking under the 57th order, Algea. The male calyx is cylindric, replete with grains; the female calyx is naked; the fruit roundish, immersed in the leaves, and many-seeded.—Of this genus there is but one species known, the pupilla, which grows naturally on the banks of ditches and rivulets, in a gravelly or sandy soil, both in England and Scotland. It grows flat upon the ground in a circle or patch, composed of numerous thin, green, pellucid, leaves, marked with a few whitish veins near the base, divided and subdivided into obtuse segments obscurely crenated on the edges. The margins of the leaves are a little elevated, but the interior parts adhere close to the ground by a fine down which answers the purpose of roots. The seeds are so small as to be almost imperceptible.