TRENTON CONGLOMERATE OF RYSEDORPH HILL 57 



Free cheeks narrow, beginning in front of the eyes with a 

 vertical, rudderlike doublure of the outer margin (fig. 27) hori- 

 zontal part forming a narrow, flat border around the eyes, which, 

 on account of the strong curvature of the eyes and the outward 

 and backward direction of its exterior margin, rapidly widens 

 posteriorly into a subtriangular, slightly convex plate. Outer 

 margin depressed, smooth, inner margin forming an elevated 

 ridge supporting the eyes. Genal spines long, narrow, nearly 

 flat, acutely pointed. Surface of free cheeks marked by liner 

 Striae directed obliquely inward and backward, becoming coarser 

 on the spine and parallel to it. 



A thorax referred to the same species has the features! of 

 the axis mostly obliterated by weathering, while the pleurae, 

 which were buried in rock, are well preserved. The axis was 

 apparently broad, about three times the width of the pleurae, 

 regularly tapering posteriorly to a small pygidial plate quite 

 strongly arched. The pleurae, 10 of which are found on either 

 side, indicating the presence of 10 body segments, are only 

 slightly bent at the beginning, but become increasingly falcate 

 posteriorly, directed backward and downward with the exterior 

 half, provided on the forward edge close to the axis with a 

 strong, projecting fulcral tubercle, the opposite point of the 

 hinder edge of the preceding pleura being furnished with a 

 corresponding deep notch, the margin of which is raised all 

 around. The pleurae are flat, with an objique furrow extending 

 from the fulcral tubercle to the tip of the point, and separating 

 the deeper posterior part from the somewhat higher anterior, 

 obliquely striated portion. 



Of the pygidium only a small roundish plate is observable. 



Dimensions. Width of cranidium 5.7 mm, length to base of 

 frontal lobe 4.5 mm; of frontal lobe 2.3 mm; length of thorax 

 10+ mm, width of thorax 11+ mm. 



Horizon and locality. Very common in the black compact lime- 

 stone pebbles, rare in the reddish gray and gray limestone peb- 

 bles of the Rysedorph hill conglomerate. (Groups 5, 6, 7) 



