There was, however, still another matter that was at that moment forcing itself upon the attention of the Commodore; and that was the doings of two craft which were pursuing the nefarious business of slavers, with a measure of audacity that was only equalled by the impunity with which they worked.  They were said to be sister ships, undoubtedly built from the same model, most probably launched from the same stocks, and made to resemble each other so absolutely in every respect, down to the most insignificant detail, that it was impossible to distinguish one from the other, excepting at close quarters.  But one was an American--named the _Virginia_, hailing from New Orleans, and manned by a Yankee crew--while the other--the _Preciosa_--sailed under the Spanish flag, and was manned by Spaniards.  They were phenomenally fast vessels, and simply laughed at the efforts of ships of the squadron to overtake them; but they had been caught in calms on three or four occasions, and boarded by means of boats; when, by a curious freak of fortune, if the boarding party happened to be British, it always proved to be the American that they had boarded; while, if the boarders happened to be American, it was the Spaniard that they found themselves meddling with.  Thus, as there was no treaty existing between Spain and the United States of America on the one hand, and England and the United States on the other, conferring mutual rights of search and capture, the vessels had thus far escaped. But now, with two such speedy craft as the _Eros_ and the _Dolphin_, it was confidently hoped that the Spaniard at least would soon be brought to book; when, there being no possibility of further confusion, it was believed that the Americans--who, in consequence of repeated disappointments, had manifested a disposition to leave both craft severely alone--might be induced to renew their interest and speedily capture the _Virginia_.