366 NEW YORK STATE MUSEUM 
for the articulation with the next segment. The gnathobase is a strong 
trapezoidal lobe connected by a contracted neck with the main body of the 
coxa. On the inner or slightly curved edge, it bears 13 relatively blunt 
teeth which decrease in size posteriorly with a slight backward direction. 
The first tooth is distinctly the largest and diverges from the others, ‘and 
the last teeth at the posterior end (the 14th and 15th of the other species) 
coalesce into a rounded lobe. The circular opening near the posterior 
Figures 77,78 Pterygotus buffaloensis Pohlman, 
Outline sketches of swimming legs. Figure 77, ventral view; 
figure 78, dorsal view 
border of the coxae which occurs in Limulus, Eurypterus and Hugh- 
milleria, has not been seen in Pterygotus. 
The second segment is short and ringlike, broadest on the posterior 
side and provided with a concave outer margin. The third appears wedge- 
like and is broadest on the anterior side; the fourth is again ringlike, 
broader than the preceding segment and broadest on the posterior side. 
The fifth segment is quite like the corresponding partin P. osiliensis, 
triangular semioval in shape, the anterior margin the longest and the 
distal margin deeply notched; the sixth segment is irregularly rhomboidal 
