The Collaborative International Dictionary
Xiphiplastron
Xiphiplastron \Xiph"i*plas"tron\, n.; pl. Xiphiplastra. [NL., fr. Gr. xi`fos a sword + plastron.] (Anat.) The posterior, or fourth, lateral plate in the plastron of turtles; -- called also xiphisternum.
Wiktionary
xiphiplastron
n. the posterior, or fourth lateral plate in the plastron of a turtle