Hi there! I saw your reply to pangur-and-grim about Belphegor, and your statement about cat breeds as coming in three basic shapes was new to me. Triangular and round seem self-explanatory to me, but I was wondering if you had other examples of square breeds?
The most immediately recognizable square breed I can think of off the top of my head is the majestic Maine Coon. Look at that big ole box.
The Pixiebob, American Shorthair, and American Curl are also pretty solidly square in my eyes. Bear in mind that calling a cat breed's shape round, square, or triangular is a bit like calling a letter/shape Kiki or Bouba - it's vibes more than it is scientific. But there are certainly characteristics common among certain shaped cats that are not common among others. As you said, round cats and triangle cats are pretty self-explanatory - square cats are those breeds that hang out somewhere in between the two.