Leaf-bases sheathing only while young, with maturity separating, except at the midrib, into a dry fibrous network which must tear or decay before the leaves fall; fruits with a stony endocarp perforated by three foramina. Family COCACEAE, p. 558. Family PHOENICACEAE This family contains a single genus of old-world palms usually associated with the fan-leaved series, and differing from all other feather-palms by having the concave side of the leaf segments turned upward. PHOENIX DACTYLIFERA Linn. Sp. Pl. 1188. 1753 The date palm was probably introduced into Puerto Rico in the early part of the Spanish occupation of the island, and isolated trees are to be found in many localities especially in the vicinity of the larger towns. The climate is, however, too cool and too moist to permit the fruit to ripen properly, and there is apparently no inducement for planting in large quantities. Family SABALACEAE Although forming no conspicuous part of the palm vegetation of the island the fan-leaved species seem to be more numerous than those of any other family. It is certain also that further species remain to be discovered, since in addition to the species listed below, young inflorescences supposed to belong to a _Copernicia_ were collected by Sintenis (no. 6512) near Utuado, and he also collected two other _Thrinax_-like palms of doubtful identity, one near Cabo Rojo and one at Fajardo. Key to the Genera of Sabalaceae Leaves depressed in the middle, with a distinct decurved midrib; a slender fiber rising from each of the notches which separate the leaf segments. INODES. Leaves flat, midrib rudimentary; segment without alternating fibers. Leaves chartaceous, naked on both sides when mature, the veinules unequal; fruits nearly sessile; seeds smooth, albumen solid except for a deep basal cavity. THRINAX. Leaves tough and coriaceous, the lower surface silvery with a persistent, closely appressed pubescence; veinules equal; fruits distinctly pedicellate; seeds deeply grooved or furrowed. Trunk tapering upward, tall and slender; pedicels short, bracteate at base; seeds subspherical, ruminate with deep narrow grooves; surface with a dull membranous cuticle. THRINCOMA.