The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Xiphisternum \Xiph"i*ster"num\, n.; pl. Xiphisterna. [NL., fr.
   Gr. xi`fos a sword + sternum.] (Anat.)
   (a) The posterior segment, or extremity, of the sternum; --
       sometimes called metasternum, ensiform cartilage,
       ensiform process, or xiphoid process.
   (b) The xiphiplastron. -- Xiph"i*ster"nala.
       [1913 Webster]