102 FIFTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



tween. The ribs terminate in a shallow groove ; heyond which, and nearly 

 in continuation, but bending a little backwards, elongate pustule-like nodes 

 correspond in number to the ribs, with two more on each side posterior to 

 the point where ribs can be counted, and a central one in a line with the 

 pygidium, making ten on each side the central one : the anterior ones are 

 longer and larger, and the posterior ones less conspicuous. Near the anterior 

 margin, the border beyond these pustules is a narrow rim which increases in 

 width anteriorly. Entire surface granulose or minutely papillose. 



The pygidium is readily recognized by the ornamented border. 



Geological formation and locality. In limestone of the age of the Upper 

 Helderberg group : Williamsville, N.Y. 



PKOETUS HALDEMANI ( n. s.). / ^V") 

 Entire body narrow, subelliptical, posterior end narrower^ length 

 -j^^^, and width at base of head -^i^^ of an inch. Head semicircu- 

 lar, with the posterior angles of the border produced : the groove 

 in front is shallow and not strongly defined, the border beyond 

 thicker and rounded; the facial suture, in its anterior extension, 

 bends outwards to a line beyond the longitudinal centre of the 

 eye, and, from this point in the furrow, bends forward to the 

 margin of the limb. Glabella ovatiB, distinctly contracted opposite 

 the anterior angles of the eyes; length a little greater than the 

 greatest width : lateral lobes marked by furrows all directed 

 .obliquely backwards; the third one cutting off the posterior angle, 

 and scarcely reaching the base. The occipital furrow is narrow, 

 and the occipital ring a little stronger than the rings of the 

 thorax. 

 Thorax neatly defined; axis prominent, the annulations of the lower 

 half directed a little forwards in the middle : lateral lobes fiat 

 as far as the geniculation of the ribs, and then bent abruptly 

 downwards in a nearly straight line, the extremities of the ar- 

 ticulations curving a little forward. 

 Pygidium neatly symmetrical, semioval, the length and width as 

 five to seven ; axis moderately elevated, gradually tapering, 

 marked by twelve or more articulations, the middle ones of which 

 are slightly undulated : lateral lobes gently convex for half their 

 width and sloping a little abruptly at the sides, with about twelve 

 ribs on each side, terminating in a shallow furrow and surrounded 

 by a plain thickened border. Two or three of the anterior ribs of 

 the pygidium extend across the furrow, and are perceptible in the 



[ September, 



