Rees Cyclopedia 1819, and therefore superceded by your source, does not list Rustia in the five pages (11 columns) on Cicada. However it does list Rustica with this description by Fabricius, in the fifth section: Genus Cercopis Fabr.
Rustica, Grey; immaculate, wings white; Fabr. An European species, found on plants.
The name Rustia looks odd to me, I would suspect it to be a misprint for Rustica. However Fabricius does not seem to be describing the same species, except that some of his specimens were very damaged, from private collections.
The following translation has a number of words which most likely have conventional meanings, but you may be able to improve it with your knowledge of the terminology. Apicalis (conical) and Lobus (lobes) are not in my dictionaries and may be modern Latin.
75 (76) Capite thoracis antico latitudine æquali,
With the head equal in breadth to the anterior of the thorax,
margine antico inter frontem et lobos verticis libere prominulos
with the anterior margin between the forehead and the clearly prominent lobes of the top of the head deeply furrowed, ( libere (clearly) literally =outspokenly) (margine antico might be better as 'front edge')
parte laterali oculos semiglobosos ferente sursum nonnihil vergente
fronte paullo prominula; rostro brevi;
with the lateral part which carries the hemispherical eyes turning somewhat upwards with the brow very slightly prominent; the mouth-parts short;
ocellis ab oculis quam inter se duplo longius remotis; alis areolis
the simple eyes twice as far from the compound eyes as the distance between them; the wings with five small conical areas.
76 (75) Capitis parte laterali horizontali, nec sursum vergente.
The lateral part of the head horizontal, and not turning upwards.