It is pointed out that searches of the Palomar Observatory Sky Survey (POSS) have provided a wealth of new astronomical objects. A description is presented of a search of POSS prints which was conducted with the objective to find large objects of exceptionally low surface brightness. It is believed that most of the objects found are examples of very old planetary nebulae. In connection with the conducted search, each POSS print was examined for several minutes without any optical aid. Descriptions of individual objects are provided, taking into account definite or possible planetary nebulae, and three objects of very low surface brightness which apparently do not have the morphology or blue central stars associated with planetary nebulae. The tentative suggestion is made that these objects are galaxies of exceptionally low projected stellar densities.