Episternum: the anterior and larger lateral thoracic sclerite between the sternum and notum.
"Explanation of Terms Used in Entomology" by John. B. Smith
In IIIA, the episternum (a) and epimeron (b) are slightly separated.
"Encyclopaedia Britannica, 11th Edition, Volume 13, Slice 4" by Various
The relations of this bone to the clavicles seem to leave no doubt that it is the equivalent of the Lacertilian interclavicle or episternum.
"The Cambridge Natural History, Vol X., Mammalia" by Frank Evers Beddard