Obscure Horror Movie Late 60s/Early 70s?

I am trying to find the name of this old horror movie I glimpsed on TV as a youngster in the late 70s. My memory is really fuzzy but I recall it may have starred Peter Cushing and it may have been a Hammer Horror Film. It was in color and I'm not sure if it was set in England. There were these strange creatures that looked sort of like mutated turtles because I remember seeing turtle-like shells and they'd fall from above like as in from trees onto their victims. I remember the victims being in a forest. Then the creatures would ooze something onto their victims and kill them. One of the characters was able to fight off a creature. Does anyone have any idea what the name of this film is? Thanks.