As I was ready to put a X on this one, I found this beautiful book starting with the letter X (and the word is not xylophone or x-ray):
Xander’s Panda Party
by Linda Sue Park
illustrated by Matt Phelan
This cute rhyming story about a panda bear planning a party at the zoo is as entertaining as it is educational. Children will learn about animals and their classifications. An author’s note at the end gives further details for children who want to investigate the subject further. Beautiful illustrations done in ink and watercolor.
I did not find any author or illustrator’s name starting with the letter X.