1. A casting apparatus, comprising: a plurality of mold flasks, each provided with at least one gaspermeable wall separating a casting chamber from a plenum chamber; a horizontal endless conveyor band for intermittently advancing said mold flasks along a closed transport path; and means selectively communicating with said plenum chambers of said flasks at selected stations of advance of said flasks along said path for pressurizing said flasks to fluidize a mold-forming medium therein and for subjecting said flasks to suction to compact said medium about a platen, said means selectively communicating with said plenum chamber being so constructed and arranged as to alternately subject each of said flasks to pressurization and suction as said flasks are advanced along said path, said plenum chambers being provided with gas fittings, said means selectively communicating with said plenum chambers including mating fittings adjacent said path and engageable with the fittings of plenum chambers of flasks registering therewith, said mating fittings being mounted upon a support member; and means for shifting said support member transversely to said path.