is 4.5 mm; the greatest width of the abdomen is 6.1 mm. The largest carapace referred to here [pl. 36, fig. 2] measures 7.4 mm in length and 10.6 mm in width. The telson figured in connection with this species measures about 27 mm in length and 5 mm in basal width.
Horizon and locality. Very rare in the dark shales of the Shawangunk grit at Otisville, N. Y.
Eusarcus (?) longiceps nov.
Plate 84, figures 1–6
Description. Carapace semielliptical in outline, about as wide at the base as long, the lateral margins nearly straight and slightly converging forward to the antelateral angles. Frontal margin well rounded; posterior margin straight transverse and genal angles acute, apparently produced a little sidewise. Eyes marginal, small, about one fifth the length of the carapace, situated at the antelateral angles, the visual surface occupying the whole eye node; the latter apparently without facets. Ocelli large, situated between the lateral eyes. The carapace was either smooth or the original ornamentation is obscured.
Horizon and locality. Frankfort shale (Schenectady beds) at Schenectady.
Remarks. We have comprised under this species a number of carapaces of strange aspect, which in outline do not agree exactly with any of the Siluric genera. The eyes, in form and position, suggest the genus Eusarcus, but the position of the ocelli near the frontal margin between the compound eyes is a feature not observed in any genus. It would seem that this form had gone even beyond Eusarcus in the concentration of the sense organs at the front, in adaptation to its habit of covering itself with mud. The type specimen [pl. 84, fig. 5] measures 18 × 15 mm, its lateral eyes are about 4 mm long, the largest specimen observed is 31+ mm long; its width is indeterminable, the sides being folded under; the eyes measure 7 mm.
