A friend on deviantART posted this challenge: draw ten different dog breeds and make them look distinct. Her reasoning is that a lot of people draw one kind of dog and that's it.
I know I draw a lot of pit bulls and I draw Dalton (a bull terrier) basically constantly, so let's try to remember the differences between those and eight other breeds with minimal or no reference.
I wound up using a reference for the poodle and the English mastiff. And to check whether Boston terriers had tails. Everything else was from memory.