_Triarthrus becki_ is usually represented as having four pairs of glabellar furrows, but the two pairs at the front are exceedingly faint and the first of them is hardly ever visible, though that it does exist is proved by a number of authentic specimens. The neck furrow is narrow and sharply impressed, continuing across the glabella with a slightly backward curvature. In front of it are two pairs of linear, deeply impressed furrows which in their inward and backward sweep are bowed slightly forward, the ends of the corresponding furrows on opposite sides nearly meeting along the crest of the glabella. In front of these, near the median line, is a pair of slight indentations, having the appearance and position of the inner ends of a pair of furrows similar to those situated just behind them. In front of and just outside this pair are the exceedingly faint impressions of the anterior pair of furrows, these, as said above, being but seldom seen. They are short, slightly indented linear furrows which have their axes perpendicular to the axis of the cephalon, and do not connect with each other or with the dorsal furrows. The latter are narrow, sharply impressed, and merge into a circumglabellar furrow at the front. In front of the circumglabellar furrow is a very narrow rounded ridge, but the anterior end of the glabella is very close to the margin of the cephalon. Specimen No. 214, which was cleaned from the dorsal side, shows the posterior tip of the hypostoma, apparently in its natural position, 3.5 mm. back from the anterior margin. The entire length of the cephalon is 6 mm., so that the hypostoma reaches back slightly over one half the length (0.583). The greater part of it has been cleaned off, and one sees the proximal portions of the antennules, which are apparently attached just at the sides of the hypostoma, 2.5 mm. apart and 2.25 mm. back from the anterior edge of the cephalon. This position is distinctly within the outline of the glabella and corresponds approximately to the location of the second pair of glabellar furrows. Specimens 214, 215, 216, 217, and 219 all seem to show the same location for the bases of the antennules. Specimen 220 is the one in which the basal shafts are best preserved and the points of attachment seem to be further apart in it than in any of the others. This specimen is 38 mm. long, and the bases of the antennules are 5.5 mm. apart and 4 mm. behind the anterior margin. As the specimen is cleaned from the ventral side, the dorsal furrows do not show distinctly, but another specimen of about the same size (No. 228, 38.5 mm. long) has the dorsal furrows 8 mm. apart 4 mm. back of the anterior margin.