PALAEONTOLOGY OF NEW YORK. 



T 11 P I D C A R 1 S , Beecher. 1884. 

 Tropidocaris bicarinata. 



PLATE XXXI, FIGS. 7-12. 



HKR. Ceratii icaridse from the Chemung and Waverly groups, etc. Second Geol. 

 1. PIT, p. 16, pi. ii. tigs. 3-5. 1884. 

 , Rthbridgb, W( id Jones. Third Rept. Committee on Fossil Phyllopoda 



of the Palaeozoic Rocks, p. 35. 1885. 



\ chorax elongate spatulate or semi-elliptical, truncate behind ; length 



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 



i of the eye, it slopes gently outward to form the rostral cleft, which is 



quite narrow. 



The Rostrum is a narrow, tree strip or plate, tapering to an acute apex; 

 longitudinally arched, bearing a strong axial ridge and two lateral ridges. 

 This body I a 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 

 making a minute posterior spine at that point. The margin on all 

 ides is broadly thickened, and the marginal sulcus is conspicuous. 



halk region, just within the principal lateral carina, bears a strong 

 which usually shows a minute depression or pit at its summit. 

 Two strong carinae extend almost the entire length of each valve, the outer 

 longer and more conspicuous, the inner usually terminating ante- 

 dorsal line just opposite the eye, but sometimes produced to 

 angle A low ridge extends from the eye to the anterior 

 similar ridge is also visible in some specimens between the 

 ina, extending tor a short distance upon the thoracic 

 On the exterior slope of the outer carina and 



