186 
PALAEONTOLOGY OF NEW YORK. 
ventral edge and passing posteriorly with the same curvature. The postero- 
ventral angle is broadly obtuse, the posterior margin slightly incurved to the 
hinge-line. The surface is evenly convex and is ornamented by a series of 
longitudinal carinae, of which five, including the marginal ridge, extend the 
entire length of the valve, four of them being prominently exsert at their 
terminations upon the posterior margin. Intercalated between these carinae 
is a series of shorter and less conspicuous ridges, beginning near the anterior 
extremity and mostly confined to the cephalic region; one or two extend 
for some distance upon the thorax. The number of ridges crossing the 
cephalic region is eleven, one of the shorter of these crossing the eye-node. 
The single valve has a length of 23 mm., and a width of 10 mm. 
Distribution. Chemung group. In the shales near the summit of the forma¬ 
tion, Warren, Warren county, Pennsylvania. 
Tropidocaris alternata. 
PLATE XXXI, FIGS. 14, 15. 
Tropidocaris alternata, Beecher. Ceratiocaridie from the Chemung- and Wavei-ly groups, etc. Second Geol. 
Surv. Penna., vol. PPP, p. 19, pi. ii, figs. 7 and 8. 1884. 
Tropidocaris alternata, Etheridge, Woodward and Jones. Third Kept. Committee on Fossil Phylloiioda 
the of Palaeozoic Rocks, p. 35. 1885. 
This species is represented only by impressions of two somewhat fragmentary 
portions of left valves of the cephalothorax. Their outline cannot be satis¬ 
factorily determined, but indications show that is does not widely differ from 
that of Tropidocaris bicarinata. These fragments are characterized by the 
numerous longitudinal ridges extending apparently the entire length of the 
valve, or somewhat interrupted and irregular in the cephalic region. These 
ridges or carinae alternate in size, the best preserved specimen showing seven 
in all, of which the larger are finely crenulate, but no other ornamentation is 
apparent on the valve. The eye-node is distinct and is crossed by the fourth' 
or middle carina. 
Distribution. Waverly group. In the sandstones at Warren, Warren county, 
Pennsylvania. 
