ALDERMANIC SPORTS FOR AUGUST.--A special meeting of the common council was held yesterday for the purpose--of proceeding in a private capacity to Coney Island to ascertain whether the clams of that region had deteriorated in quality since their last visit. This they did in company with other gentlement, in Husted and Kendall's big stage, and as we are informed had a right merry time. After sufficient discussion in committee of the whole, a resolution was, (or ought to have been) passed, that clams are rather pleasant fodder. We coincide in that resolution, nem clam.
--Brooklyn Daily Eagle, Friday, August 25, 1848
Alderman is kind of an old-timey-sounding term, isn't it? The definition meant here is likely talking about city legislators (see Miriam-Webster's definition). http://www.merriam-webster.com/dictionary/alderman
"Nem clam" is a pun, it appears. "Nem. con." is a Latin abbreviation for "without dissent."