This curious little palm is only eight or ten feet high, and has the stem slender, ringed, and armed with strong conical spines. The leaves are rather small and few in number, and the leaflets are much shorter, broader and more rigid than in any other palm of this genus. The petioles are long and rather thick, much sheathing at the bases which are persistent, clothing the stem some distance down after the leaves have dropped away from them, a character not found in any other prickly stemmed species. The spadix is very long, branched and drooping. The fruit was not seen. I only met with this palm on the Upper Rio Negro in two localities on the sandy margins of rivers and lakes just above the limits of the winter floods. Genus LEPIDOCARYUM, _Martius_. Male flowers on one tree, female or hermaphrodite flowers on another. Spathes, imperfect, bract-like, tubular sheaths. The male flowers have six stamens. The female flowers have three sessile stigmas and six imperfect stamens. The stems are very slender, unarmed with spines or tubercles and deeply ringed. The leaves are fan-shaped, and have slender petioles and long swollen sheaths. The spadices are elongate and pinnately branched, growing from among the leaves. The fruits are oblong and covered with imbricated scales. These delicate and very rare little Palms scarcely differ botanically from the last genus. Two species only are known, inhabiting the dense virgin forests of the Upper Amazon and Rio Negro, where they appear to be very locally distributed. [Illustration: Pl. XXII. W. Fitch lith. Ford & West Imp. LEPIDOCARYUM TENUE Ht. 8 Ft. ] PLATE XXII. LEPIDOCARYUM TENUE, _Martius_. Caranaí do Mato, _of the Rio Negro_. This, the smallest of the fan-leaved Palms, has a smooth, ringed, waving stem as thick as one’s finger and six or eight feet high. Its dark green glossy leaves, with narrow drooping leaflets, grow on long and slender stalks which have their sheathing bases much swollen and lengthened. The spadices are small and slender, and the fruits, which are not abundant, are scaled in the same manner as those of the Mauritias, and are about the size of a large hazel-nut. This rare and elegant species grows in the gloomiest depths of the virgin forest of the Upper Rio Negro, generally at some distance inland from the rivers, and shaded by the loftiest forest trees. Plate II. fig. 4. represents a fruit of this species of the natural size. Genus GEONOMA, _Willdenow_. Male and female flowers on distinct trees, or rarely on distinct spadices of the same tree. Spathe small, incomplete. Male flowers with six stamens and a rudimentary pistil. Female flowers with three stigmas and a six-toothed ring of abortive stamens.