1) Straight-jawed 
• (a.) Having the front of the head, or the skull, nearly perpendicular, not retreating backwards above the jaws; -- opposed to prognathous. See Gnathic index, under Gnathic.
Or·thog'na·thous adjective [ Ortho- + Greek ... the jaw.] (Anat.) Having the front of the head, or the skull, nearly perpendicular, not retreating backwards above the jaws; -- opposed to prognathous . See Gnathic index , under Gnathic . 
orthognathous 1. Having the lower jaw in line with the upper jaw. 2. Having straight jaws.
mouthparts are directed downwards from the head from the insect's normal position
straight-jawed; having the profile of the face vertical or nearly so; having a gnathic index below 98.