184 
PALEONTOLOGY OF NEW YORK. 
TllOPIDOC Allis, Beecher. 1884. 
Tropidocaris bicarinata. 
PLATE XXXI, FIGS. 7-12. 
Tropidocaris bicarinata, Beecher. Ceratiocaridse from the Chemung and Waverly groups, etc. Second Geol. 
Surv. Penna., vol. PPP, p. 16, pi. ii, figs. 3-5. 1884. 
Tropidocaris bicarinata, Etheridge, Woodward and Jones. Third Rept. Committee on Fossil Phyllopoda 
of the Palaeozoic Rocks, p. 35. 1885. 
Cephalothorax elongate spatulate or semi-elliptical, truncate behind; length 
one and one-half times the width. Hinge-line straight, nearly as long as 
the greatest length of the shield. Toward the anterior extremity, just in 
front of the eye, it slopes gently outward to form the rostral cleft, which is 
quite narrow. 
The Rostrum is a narrow, free strip or jilate, tapering to an acute apex; 
longitudinally arched, bearing a strong axial ridge and two lateral ridges. 
This body has been observed in two instances in such a position and of 
such form as to leave little doubt of its function. 
The anterior extremity of each valve is produced into a minute spine at 
the dorsal line; at its base the margin is transverse for a short distance, 
rounding in a broad curve to the ventral and posterior edges. The poste¬ 
rior extremity is broadly truncate, the margin rounding over the postero- 
ventral angles, curving inward toward the hinge-line, and outward at the 
hinge, making a minute posterior spine at that point. The margin on all 
sides is broadly thickened, and the marginal sulcus is conspicuous. 
The Cephalic region, just within the principal lateral carina, bears a strong 
optic node, which usually shows a minute depression or pit at its summit. 
Two strong carinae extend almost the entire length of each valve, the outer 
one the longer and more conspicuous, the inner usually terminating ante¬ 
riorly near the dorsal line just opposite the eye, but sometimes produced to 
the anterior angle. A low ridge extends from the eye to the anterior 
extremity and a similar ridge is also visible in some specimens between the 
eye and the inner carina, extending for a short distance upon the thoracic 
portion of the carapace. On the exterior slope of the outer carina and 
