Dear Jackie: I think "parafango" would be what you call "modeling clay".

I also seem t recall name "plasticene". I couldn't find "plasticene" on Internet, but did find ad for a massage parlor offering: specializes in body therapies such as body scrubs,
parafango, mud treatment facials, massage, waxing, laser hair removal, and micro-derm abrasion.

On a second search I found:Notebook
... Nonhardening Modeling Clay / Plasticene or Plastilene.
Probably the most widely used of the three ...
http://www.noteaccess.com/MATERIALS/Matplasticene.htm