Morgan Expeditions. 113 



ginal fold strongly convex and of moderate wiflth. Eyes large and 

 very prominent, situated exactly opposite outer extremities of anterior 

 and median lobes. In none of the specimens in the collectiou are they 

 sufficiently well preserved to allow of detailed description. 



A Hypostome, probably of this species, is sub-quadrate in form and 

 strongly convex." The front margin is strongly arched and slightly sub- 

 angular. On each side it is produced in a short acuminate spine, ex- 

 tending directly outward. The sides are nearly straight and incline 

 slightly toward one another in going backward. The body of the hy- 

 postome is very convex and abruptly separated from a flattened margin. 

 The outline of the convex portion forms a very regular curve as follows : 

 beginning at the anterior lateral angles it runs obliquely backward and 

 inward, the flattened margin widening gradually ; posteriorly with a 

 regular arch it extends apparently nearly to the margin. The whole 

 hypostome is strongly arched, transversely and vertically. The abrupt 

 margin of central portion increases in height going backward. This 

 specimen measures 7 mm in length and about 10 mm in greatest width. A 

 fragment of a larger specimen of hypostome, having a length of 21 mm , 

 was also obtained from the same bed as the above, and, although dif- 

 fering from it somewhat in appearance, may belong to an older specimen 

 of the same species. 



Pygidium triangular, with curved sides, and very convex. Axis nar- 

 row, prominent, regularly rounded from side to side, and extending 

 about 3-4 length of shield ; width in front apparently equal to 1-3 width of 

 shield. It decreases slightly in width and gradually in height posteriorly, 

 where it ends abruptly, the extremity being rounded and convex; width 

 in front about one and one-half to two times the width behind. In one 

 large specimen the axis shows 14 rings, the anterior of which, in the 

 internal mould, are prominent, rounded, and separated by furrows of 

 rather greater width ; but they become very small and indistinct pos- 

 teriorly, the last three or four being crowded together. In none of the 

 specimens collected is the articular ring preserved, but several of these 

 show 11 to 13 rings. Lateral lobes convex, but generally of much less 

 elevation than the axis; margin slightly flattened. Furrows deep and 

 extending to the margin in all but the last four or five rings. The segments 

 are rounded near the axis, but are flattened and much broader toward 

 the margin. The anterior one is nearly at right angles with the axis, 

 but they become more strongly inclined posteriorly. On the first seg- 

 ments the sutures are faint and on the posterior ones not observable. 

 The margin is denticulate, the terminations of each segment being ap- 

 parently blunt and obliquely rounded or angular. Posterior part of 

 pygidium, behind axis, highly inclined, rounded and smooth; posterior 

 margin concave, arched and slightly turned up along the edge. A spec- 

 imen of medium size measures in length, about 15 mm , in width, 14 mm . A 

 very large specimen has a length of 32 mm . 



A few detached segments, that may belong to the thorax, were found, 

 but they are unsatisfactory for determination. 



