from the Upper Devonian Rocks of Ohio. 37 
minates a little within the margin opposite the longest part of 
the valve. A second and slightly stronger ridge rises from 
just behind the middle of the length of the hinge, descends with 
a gentle forward curvature, and terminates near the upper 
anterior end of the first one. The anterior or principal tubercle 
creasing in length backward from the first or anterior segment. 
Telson proportionally large, of a general triangular form, 
but slightly protruding at the origin of the movable spines, 
4 behind into a long, slender, and apparently 
Fi 
pada shales (Portage and Chemung), at Leroy, Lake County, 
io. 
