The Collaborative International Dictionary of English v.0.48:

Entoplastron \En`to*plas"tron\, n.; pl. Entoplastra. [Ento- +
   plastron.] (Anat.)
   The median plate of the plastron of turtles; -- called also
   entosternum.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Entosternum \En`to*ster"num\, n.; pl. Entosterna. [NL. See
   Ento-, and Sternum.] (Anat.)
   See Entoplastron. -- En`to*ster"nal, a.
   [1913 Webster]