Do you have that book on hand? That is just a typo, by the way. His name was Bartolomé de las Casas, and that can be seen all over the place, like in this edition of his "Brevísima relación" from his own time.

http://bdh-rd.bne.es/viewer.vm?id=0000128950&page=1

You may occasionally see his name written as "Bartholomé" instead of Bartolomé, but that is just a small orthographic difference, with Bartholomé being a more archaic version, and Bartolomé being the modern normalised orthography.

The bishop's own signature is less of use in this case, as he used an abbreviated version, normally "Fr. Bme. de las Casas", as shown in these two examples:

http://pares.mcu.es/ParesBusquedas20/catalogo/show/126836

http://bdh-rd.bne.es/viewer.vm?id=0000023195&page=1

Anyways, "Barlolomé" is not a Spanish name, and never has been.