5. _Spongia virgata._ (Slender sponge.) Nearly branched, smooth, fulvous, stem divided, slender, cylindrical, knobby, branches erect, slender, nearly heads acute; pores unequal, irregular, small. A small species, three inches high, found at Oysterbay, on rocky bottoms, rare; stem with few branches, and imperfect ones, like knobs. Substance stupose. Branches round, alternate, small. Pores without any determinate shape. ART. XII. _Memoir on the Xanthium maculatum, a New Species from the State of New-York, &c. by_ C. S. RAFINESQUE, ESQ. Pursh and Michaux mention only one species of American _Xanthium_, the _X. strumarium_, while there are three noticed in the catalogue of Dr. Muhlenberg, the above species, and the _X. orientale_, and _X. spinosum_. The first and the last are natives of Europe, and have been naturalized in the United States, with many other plants. The species called _X. orientale_ by Dr. Muhlenberg, appears however to be a native; but the _X. orientale_ of Linnæus, is a native of Siberia, Japan, and the East-Indies; and when plants are found to grow in such opposite quarters of the globe, a strong presumption arises that they are not identical species, which presumption has been confirmed by experience in many instances, whenever the plants of both countries have been accurately examined. Decandolle, in the French Flora, (2d edit, of 1815.) vol. 6. p. 356, describes, under the name of _X. macrocarpon_, a species found in France, and which he takes to be the real _X. orientale_ of Linnæus. He has changed its name, because, he says, that it is not certain that the _X. orientale_ grows in Asia; or, if any grows there, that it is identic with his species; which, however, is really the _X. orientale_ of Linnæus, Son, Lamark, and Gaertner. He adds, that he possesses in his herbarium, a species from Canada, different from his _X. macrocarpon_ which has been figured by Morison, on whose authority some authors have asserted that the _X. orientale_ grew in Canada, mistaking his figure for that plant. From the above statement, it appears that much obscurity and difficulty arises in botany, when errors creep into the distinction of species: to detect those errors, and to ascertain the synonyme of obscure species, is not one of the least useful botanical labours. Having found, last year and this year, in the neighbourhood of New-York, a species of _Xanthium_ different from any described by the authors, and intermediate between the _X. strumarium_ and _X. orientale_ of Linnæus, I presume that it may be the _X. orientale_ of Muhlenberg, Leconte, and Morison, and the _Xanthium_ of Canada, mentioned by Decandolle, Dumont, &c. I have given to it the name of _X. maculatum_, since the stem is spotted like the _Conium maculatum_. None of those authors having described it, I suppose that its description will be acceptable, and will serve to fix this new species among the American botanists.