THE EURYPTERIDA OF NEW YORK 257 
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 Shawan- 
gunk 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; pos- 
terior margin straight transverse and genal angles acute, apparently pro- 
duced a little sidewise Eyes marginal, small, about one fifth the length 
of the carapace, situated at the antelateral angles, the visual surface occu- 
pying the whole eye node; the latter apparently without facets. Ocelli 
large, situated between the lateral eves. The carapace was either smooth 
or the original ornamentation is obscured. 
Horizon and locality. Frankfort shale (Schenectady beds) at Sche- 
-nectady. 
Remarks. We have comprised under this species a number of cara- 
paces 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 x 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. 
