DECISION.
Ex Parte.......................} Before the Chief Justice of the
.....................................} Supreme Court of the United
John Merryman.........} States at Chambers.
I added dots to preserve the spacing of the original. At Chambers rulings are rulings of the Justice as a Justice of the Supreme Court. The signature on the ruling is "R. B. Taney, Chief Justice of the Supreme Court"
Go back and read the decision again. Better yet, read a book like "Lincoln and Chief Justice Taney: Slavery, Secession, and the President's War Powers" by James Simon for a short but more than adequate overview of the case. Chief Justice Taney was acting in his position as head of the Circuit Court that included Baltimore. His ruling was issued from that bench, not the Supreme Court bench. A single justice cannot speak for the entire court, and the entire court never took up the case.