The lower surface is clothed with a satiny, appressed grayish pubescence somewhat less pronounced than that of _Thrincoma alta_. As in that species the veinules are of equal size, but they are more widely separated, and the wavy and usually somewhat oblique transverse veinules are easily distinguishable on both sides of the dried leaf. There are also slight traces of wax on the ligule and in the grooves of the upper surface. The median divisions are united for distinctly more than one-third their length. The spathes and spadix are distinctly larger than those of _Thrincoma alta_, but the fruits are, unfortunately, quite immature and contain only shriveled seeds. The pedicels of the fruits are 2–4 mm. long and bear, usually near the middle, a very slender bract 1–2 mm. long. This species is apparently distinct from _Thringis laxa_ in the larger size and firmer texture of the leaves. It differs in the longer pedicels of the fruits, with their longer and more slender bracts, from a specimen belonging to the New York Botanical Garden and supposed to have been collected by Mr. A. A. Heller, though the number (3278) indicates that it may belong to the Sintenis series. This consists of a single, short, once-branched inflorescence arising from two fibrous spathes. The fruits are about 4 mm. in diameter, nearly spherical, distinctly apiculate, deep reddish brown in color and borne on pedicels 2–3 mm. long, with a bract 1 mm. long or less at or below the middle. The seeds are 2–2.5 mm. in diameter; the surface is smooth and shining and light brown in color; general shape spherical but with deep folds and convolutions. No leaves are known in connection with this specimen, and the exact locality is also in doubt. Mr. Heller believes, however, that the inflorescence came from a small _Thrinax_-like palm growing in the limestone hills a few miles to the east of San Juan. Family ARECACEAE A large family, with abundant genera in the tropics of America and Asia, but absent from tropical Africa. The Puerto Rico representatives may be recognized very easily by the fact that the leaf crown is supported upon a column of the sheathing bases, a character of which the royal palm furnishes a conspicuous and ever-present example. Of the remaining genera, one, the betel palm of the East Indies is sparingly introduced about towns in the western part of the island and may be recognized at a glance by reason of the extremely dark green of its foliage. The other two genera are native palms confined to uncultivated areas and thus seldom seen at close range from traveled roads. The mountain palm, _Acrista_, covers the summits of many of the mountains of the island, but _Aeria_ seems to be confined to the range of high limestone crags which skirt the northern coast of the island between Bayamon and Arecibo. Key to the Genera of Arecaceae