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Fig. 90.—Thorax of Telea polyphemus, side view, pronotum not represented: em, epimerum of prothorax, the narrow piece above being the prothoracic episternum; ms, mesoscutum; scm, mesoscutellum; ms″, metascutum; scm‴, metascutellum; pt, a supplementary piece near the insertion of tegulæ; w, pieces situated at the insertion of the wings, and surrounded by membrane; epm″, episternum of the mesothorax; em″, epimerum of the same; epm‴, episternum of the metathorax; em‴ epimerum of the same, divided into two pieces; c′, c″, c‴, coxæ; te′, te″, te‴, trochantines; tr, tr, tr, trochanters. A, tergal view of the mesothorax of the same; prm, præscutum; ms, scutum; scm, scutellum; ptm, postscutellum; t, tegula.

The præscutum and postscutellum are usually minute and crowded down out of sight between the opposing segments. As seen in Fig. 90, the præscutum of most moths (Telea) is a small rounded piece, bent vertically down so as not to be seen from above. In Polystœchotes and also in Hepialus the præscutum is large, well-developed, triangular, and wedged in between the two halves of the scutum. The postscutellum is still smaller, usually forming a transverse ridge, and is rarely used in taxonomy.