Edit in JSFiddle

var contacts = new Backbone.Collection([
    {firstName: 'Luke'},{firstName: 'John'},
    {firstName: 'Bill'},{firstName: 'Jill'}
],{model:Backbone.Model});

//remove the Luke model from the collection
contacts.remove(contacts.findWhere({firstName:'Luke'}));
//remove array of model instances
contacts.remove([
    contacts.findWhere({firstName:'John'}),
    contacts.findWhere({firstName:'Bill'})
]);

//Verify the that the model's were removed
console.log(contacts.pluck('firstName')); //logs ["Jill"], Luke, John, Bill were removed