A genus of palms distributed through tropical America from Mexico to Cuba and Paraguay. All the species are of stocky, compact growth, with a dense crown of numerous leaves. The trunk and the leaf-stalks are usually armed with strong, sharp spines, sometimes several inches long. Although totally different on close inspection this genus has in Puerto Rico a superficial resemblance to the royal palm, which often deceives travelers. The similarity lies mostly in the two facts that both the royal and corozo palms are more robust and stiffly erect than the cocoanut, and that the leaf-divisions instead of lying horizontal and in one plane are tilted at different angles to the midrib, thus giving the foliage seen in the mass a somewhat unkempt appearance in comparison with the cocoanut. In distinguishing the corozo palm from the royal palm when seen at a distance so great that the spines of the one and the columnar green leaf-sheaths of the other can not be seen, recourse may be had to the following facts. The leaf crown of the corozo palm is much rounder, thicker and more compact than that of the royal palm, since it contains many more leaves, and these persist much longer. The royal palm can also be known by the unopened leaves which project straight upward like flag-poles or lightning-rods, while in _Acrocomia_ the leaves open as they are pushed out and seldom offer a suggestion of the spire-like effect. =Acrocomia media= sp. nov. Trunk 20–30 cm. in diameter near the base, thickened above to 50 cm. or less; height commonly about 6–8 m. rarely exceeding 10 m. Surface of trunk with slight annular impressions. Internodes armed with slender black spines, the larger 10–15 cm. long, mostly confined to the lower half of the internodes. Fruit green, becoming yellowish, the husk firmly fibrous, inedible; about 35 mm. in diameter, nearly spherical in shape, with a distinct apical papilla. Kernel 25 mm. wide by 22 mm. long; width of the cavity 18 mm. The type specimen was collected near Ponce (photograph no. 255). The _Acrocomia_ of Puerto Rico seems to differ from _A. aculeata_ (Jacquin) in its robust habit and somewhat bulging trunk, while it is less stout and less swollen than _A. fusiformis_ (Swartz). The name _Acrocomia lasiospatha_, although used by Martius and Grisebach has no warrant for supplanting _fusiformis_ of Swartz, which must be preferred for the Jamaica species with the thick, swollen trunk.