Two great and entertaining stories. The Futurological Congress, an SF story, is still believable despite being written 40 years ago. Sometimes, the old SF may be feeling fake, but not this time. (un)fortunately. A lot of neologisms, making from time to time reading it difficult. This story was an inspiration for The Congress, a 2013 film directed by Ari Folman.
The Mask is a hunt story that isn't too dynamic and more filled with thoughts and thinking. But this is what makes it great.
A great read not only for SF fans but for those who're interested in human psyche as well.