90 PROCEEDINGS OE THE ACADEMY OP 



lateral angles, wliich are not truncated. Mesial lobe rather de- 

 pressed, but rounded and well defined, narrow, or only about 

 two-thirds as wide at its anterior end as the lateral lobes, taper- 

 ing gradually, witli straight sides, to its posterior extremity, 

 which terminates at a distance of about half the breadtli of the 

 anterior end, within the margin ; provided with about twelve or 

 thirteen nearly straight segments, most of wliich are well defined. 

 Lateral L^bes gently convex, sloping gradually from near the 

 middle to tlic lateral and posterior margins, which are horizontally 

 flattened, but not thickened; segments eight or nine, not extend- 

 ing upon the flattened margins, and each divided its entire length, 

 by so broad a furrow (flat within) that only a very narrow ante- 

 rior and posterior margin is left projecting, and merely separated 

 from that of the contiguous segment by a faint linear depression, 

 tlius presenting the appearance of narrow ribs or segments longi- 

 tudinally marked by faint linear furrows, and separatevl from each 

 other by broad flattened depressions. Surface apparently nearly 

 smootli. (Other characters unknown.) 



Length of pygidium, 0.G4 inch ; breadth, 0.94 inch ; height of 

 lateral lobes, 0.13 inch; do. to top of mesial lobe at its anterior 

 end, 0.23 incli. 



The pygidium of this species seems to present much the same 

 proportions as the corresponding part of P. Haldemani, Plall 

 from the Hamilton group ; but it has a proportionally^ narrower 

 mesial lobe, and a smaller number of segments in the lateral 

 obes. It also differs in having a distinctly flattened instead of 

 thickened border. If I have correctly understood the nature of 

 the segments of its lateral lobes, they are also A^ery different from 

 those of P. Haldemani, being provided with wide flattened longi- 

 tudinal furrows. These furrows are so wide and strongly defined 

 that I have been in some doubt whether the}'" ought not rather to 

 be regarded as the divisions between the segments (wliich, in that 

 case, would be represented by the comparatively narrow interven- 

 ing furrows) than as the furrows of the segments themselves. 

 On tracing them inward, however, to the mesial lobe, they are 

 found to be abruptly narrowed and curved slightly forward as 

 they approach the latter, so as to seem to correspond to the 

 furrows on the segments, rather than to depressions hehveen them. 



None of the specimens show much of the surface, but, as far as 

 it can be seen, it seems to be smooth, and to coincide exactly 



[July 4, 



