1. Inner cloyster - An internal conglomerate of fecal matter that may have taken years to accumulate in the lower bowel.
These are typically "high quality cloysters" and are usually much smaller in size and denser than outer cloysters.
2. Outer cloyster - often occuring on people who have not had a shower for a couple of weeks. These are also often referred to as "inferior cloysters" and are usually dry and light in colour.
Note: There may also be a book detailing the physical properties and variation of cloysters and details how to grow your own.