New York, Dec. 1. - An arrest which the pólice believe to be a very important one was made in the general postoffice Tuesday. The prisoner is Richard G. Monks, alias Wellington Thornewaite, who is wanted for forgery in Bay City, Mich., and if the contents of his pockets show anything he has been operating on a very extensive scale. There were found on him blank checks on at least 200 banks in states all the way from Texas to Maine. He also carried a punch such as Is used in banks for punching checks, and a loaded revolver. The prisoner, who is a good looking, well-dressed man of 21 years, had in his pocket a key to a room in the Iroquois hotel in Buffalo, and he had just come from that city. Among his possessions were also found pictures of two very beautiful young women. The pictures had been taken in Ypsilanti, Mich. Monks will be held to await requisition papers.