scutum, scutellum, scutella, scutellar

scutum noun - the anterior portion of the mesonotum, especially when enlarged (in certain groups) and forming most of the dorsal surface of the thorax.

scutellum noun, plural scutella, adjective scutellar - the third section of the upper surface of a segment, very prominent on the thorax, especially in Coleoptera (beetles) of which it is the only visible portion of the mesonotum. It is also prominent in many true bugs, Heteroptera. The scutellum typically forms a little triangle at the base of the folded wings, pointing towards the tip (apex) of the abdomen.

Also: any small, shield-like sclerite.

Photos showing a prominent scutellum:

Divisions of thorax (front | middle | rear):

prothorax | mesothorax | metathorax

Dorsal surface of thorax (notum):

pronotum | mesonotum (scutellum) | metanotum

Lateral (pleural) surface of thorax:

propleuron | mesopleuron | metapleuron

Ventral surface of thorax:

prosternum | mesosternum | metasternum

Gordh, A Dictionary of Entomology, p. 820 (1)