FIGURE 2. Schematic of a typical Stegonotus head (specifically, the head of the holotype of S. ayamaru, RMNH.RENA 31199) to illustrate the head-scale pattern and some character definitions. (A) Dorsal view. Labeled head scales include internasals (IN), prefrontals (PF), frontal (F), supraoculars (SO), and parietals (P). Numbered points include (1) the anterior contact point of the internasals; (2) the posterior contact point of the internasals; (3) the anterior contact point of the prefrontals; (4) the posterior contact point of the prefrontals; (5) the posteriormost point of the frontal, where the posterior edge of the frontal meets the parietal suture; (6) the two points where frontal, parietal, and supraorbital meet; and (7) the two points where parietal, supraorbital, and postorbital meet. Our measurements of internasal suture lengths are taken as the straight-line distance from Point 1 to Point 2, of prefrontal suture lengths from Point 3 to Point 4. The posterior frontal angle (PF<) is defined by a vertex at Point 5 and rays extending from Point 5 through Point 6 on either side of the head. The anterior parietal angle (AP<) is defined by a vertex at Point 6 and two rays, one extending from Point 6 through Point 5 and the other from Point 6 through Point 7. The latter is what we call the lateral ray, and its orientation relative to the midline of the head, shown as a dotted yellow line, is of diagnostic value. The red line indicates how we evaluate the lateral ray, considering it laterally oriented (when the angle of the red line with the midline of the head is 90° ± 10°) or posterolaterally oriented (when the angle of the red line with the midline of the head is <80°). (B) Ventral view of the holotype of S. ayamaru to illustrate the arrangement of the mental (M), first infralabial (IL1), anterior and posterior genial scales (AG and PG, respectively), and of the gular scales separating the genials and the first gastrostege (G1). There are four rows of gulars (labeled with Roman numerals I–IV). ...