The Ocean Mail Service of the United States, consists of eight lines, and twenty one steamers in commission, with an aggregate tonnage of 48,027 tons. Three of these lines are transatlantic; the Collins, the Havre, and the Bremen. Two connect us with our Pacific possessions, and incidentally with Cuba and New-Granada. They are however indispensable lines of coast navigation. One connects the ports of Charleston, in the United States, and Havana, in Cuba, another connects New-Orleans with Vera Cruz, and another connects Havana and New-Orleans. Beyond these, we have a line of two steamers running between New-York and New-Orleans, touching at Havana, and one steamer touching at the same point between New-York and Mobile. Also four steamers between New-York and Savannah, four between New-York and Charleston, two between New-York and Norfolk, two between Philadelphia and Savannah, two between Boston and Baltimore, four between New-Orleans and Texas, and two between New-Orleans and Key West. All of these are coast steamers of the best quality; and some few of them have a nominal mail pay. We have also several transient steamers which have no routes or mail contracts, and which are consequently employed in irregular and accidental service, or laid up. They are the Ericsson, the Washington and the Hermann, the Star of the West, the Prometheus, the Northern Light, the Daniel Webster, the Southerner, the St. Louis, laid up in New-York; the Uncle Sam, the Orizaba, and the Brother Jonathan, belonging to the Nicaragua Transit Company, and the California, Panama, Oregon, Northerner, Fremont, and the tow-boat Tobago, belonging to the Pacific Mail Steamship Company, all lying in the Pacific. Also the Queen of the West, Mr. Morgan's new steamer, in New-York. These, like all other American steamers when unemployed on mail lines, generally lie in port for want of a remunerative trade. (_See Paper A._)