Page:Second Geological Survey of Pennsylvania Report of Progress PPP.djvu/25

 and occupying about a fourth of each valve. This area is ornamented in each valve with a prominent rounded tubercle at its posterior dorsal apex; and a large rounded elevation occupying the whole anterior end of the valve, making in all four prominent elevations on the cephalic area. The optic node is situated on the lower side of the largest tubercle and adjacent to the limiting furrow.

The thoracic portion of the valve is ornamented with an elongate tubercle near the middle of the anterior portion, produced into a nodose ridge following the contour of the lower margin and dying out before reaching the posterior end. A similar tubercle, but situated transversely, is found in the upper dorsal portion, and is continued in a nodose ridge adjacent to the dorsal line, and along the posterior margin of the valve. In the center of the area partially enclosed by these two ridges is a less prominent longitudinal row of minute nodes forming a third carina.

The valves are also ornamented with minute irregular tubercles on the summits of all the elevated portions of the valves, a single row appearing along the three ridges and around the extreme margin of the posterior portion.

composed of six naked segments, which become more elongate towards the telson. Somites cylindrical, marked by a thickened rim on the anterior end; ornamented with four or more spinose nodes across the middle of the dorsal side, and by a row of smaller retral spines or nodes around the posterior dorsal margin.

short, triangular, produced behind into a slender, acute, carinate spine, having a length equal to one-half the abdomen; also two lateral movable spines, extending as far as the prolongation of the telson. Test thin.

The largest carapace observed has a length of 18 mm., and a width of 10 mm. A single cercopod belonging to a large individual has a length of 25 mm. A small entire example has a total length of 16 mm., of which 6 mm. pertain to the carapace, 6 mm. to the abdomen, and 4 mm. to the telson and spine.

This species is more highly ornamented than any yet described, and is the only one of the genus observed in the