There is no official description of ewes, but it is reasonable to say that wool quality is of paramount importance.
Here is a classic Nocton ewe from the 1950's
This is a classic Messingham ewe from Mr Bird's famous flock in the 1960's.
This picture from the 1900's shows the quantity of outstanding ewes that were around in those days.
Lisette Smith demonstrates a high quality ewe at the Royal Show.
Tom Booths Ewe demonstrates why it's called a Longwool.