THE EURYPTERIDA OF NEW YORK 289 
Carapace elongate oval in outline, broadest in the posterior fourth, 
whence it contracts to half the width at the frontal margin. Its length 
and greatest width are but slightly different. The lateral margin is most 
convex at the broadest portion of the carapace which is frequently some- 
what expanded into a kind of cheek. It becomes gently convex more an- 
teriorly and passes rather abruptly at the antelateral angles into the 
more or less projecting frontal margin. The postlateral angles are well 
rounded and the posterior margin is deeply concave in the middle. The 
frontal border is furnished with a row of 8-16 acute denticulations which 
are longest in the middle and decrease in size toward the lateral ends. 
The serrae are directed obliquely upward. The lateral margins are bor- 
dered by a thickened rim. 
The upper side of the carapace is highly sculptured. Its most promi- 
nent parts are the big bulging compound eyes. The portion of the carapace 
in front of these is flat but rises in the middle to a large subcircular mound, 
bearing tubercles of greater size than those forming the ornamentation 
of the rest of the carapace. Oval, sharply set-off cheeklike ridges ex- 
tend backward from the lateral eyes to near the posterior margin, and 
from the intervening depression, midway between the lateral eyes, rises 
the very prominent small mound bearing the ocelli. The underside of the 
carapace bears a broad and thick doublure which is widest along the 
frontal margin and there exhibits a deep concentric furrow. © 
The lateral eyes are very large (one third the length of the carapace), 
forming projecting elliptical bodies that lie near the lateral margin and 
parallel to the latter in their major axis, thus converging strongly forward. - 
Their posterior extremities lie approximately on the transverse bisecting 
line. The visual surface is crescent-shaped and narrow; its horns approach 
each other on the inner side. The eye mound overtops the visual surface 
considerably and forms apparently an overhanging ridge on the inner 
side of the visual surface so that the latter frequently disappears entirely 
in compressed specimens. | 
The ornamentation of the carapace consists of small tubercles which 
