legs(dog,1).
legs(spider,8).
animal(dog,blackie).
animal(dog,spot).
animal(spider,charlotte).
animal(spider,ralph). 

countlegs([],Count,FinalCount):- FinalCount = Count.
countlegs([AnimalName|RestOfList],Count,FinalCount):- 
    animal(Type, AnimalName), legs(Type,NumLegs),
	NewCount is Count + NumLegs,
    countlegs(RestOfList, NewCount, FinalCount).