I have two female litermates that are about 9 years old.  One of these
cats(or at least I think it is only one of them) leaves me a gathering of
nickle sized turds on the floor next to the liter box about every other day.
They are pretty much dried up when deposited.

This started after I started feeding them a dry Science Diet food for
reducing hair ball incidents.  I was only feeding this once a day, and was
feeding them their regular canned food once a day.  I have taken them off of
the dry hairball stuff and put them back on the strictly canned food diet.

Both cats are otherwise healthy and very playful.  Their play among
themselves gets pretty rough, but that has been the way they play with each
other since day one. They are very gentle when they play with my wife or me.

They were not box trained when we got them so my wife did that task.  They
both urinate in the box (the cats, not my wife!).  The cats use the same
box, and always have.

They are Persian/fence-jumper mixed breed.

Any ideas?

Thanks for your help!

Just call me "turd wrangler"..."TW" for short.