Sounds just like a lime.

From the information you have given, it is really not all that possible to pin-point exactly what your tree's identity is. However, Casa Del Gatos, could easily be correct, as the tree is bushy and does not have the tall/erect growth pattern of most lemons. Find a thread on this forum by Malcolm Manners and click on his "my page", then click on the citrus leaf identification addy and compare your tree's unknown leaf with the leaves that are shown on Dr. Manners web site. - MIllet

Additionally....The tree has long thorns, because it was started from a seed. Most all citrus "seedlings" develop many long and sharp thorns. Take care. - Millet