238 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
the point where the pleura begin to taper into spines. These grooves 
occupy a much larger proportion of each pleuron than do those of — 
P. harlani. The terminal spines appear to be rather longer and more 
slender than in P. harlani. The second spine is not longer than the — 
others. 
The pygidium differs strikingly from that of P. harlani, and is the 
one figured by Walcott (Loc. cit., pl. 8, fig. 1d). This pygidium 
differs from the one found on entire specimens of P. harlani in being 
broader than long, and in having the axial lobe distinctly rounded in- 
stead of triangular. The last five segments of this specimen (M. C. Z. 
No. 20) are much longer than those on the average specimen of P. 
harlant, and it is seen from the small entire specimen in the collection 
of Mr. W. P. Haynes that it belongs to P. haywardi. A second 
pygidium of this type is in the M. C. Z. (No. 652) and a third in the 
Geological section of the M. C. Z. A nearly entire specimen which is 
in the collection of Mr. Winthrop P. Haynes has seventeen thoracie 
segments and shows that the short pygidium assigned above to this 
species really belongs to it. Mr. Haynes’s specimen is largely exfoli- 
ated, and the substance of the pygidium is entirely gone. Its outline 
is, however, indicated on the matrix, and it is of the broad short type, 
apparently 9 mm. long and 15 mm. broad. The whole trilobite is 
about 105 mm. long and is quite narrow, the thorax being about 
55 mm. wide at the first segment. 
Typrs.— As the holotype of this species I have selected cranidium 
No. 16 (Plate, fig. 1) recently presented to the M. C. Z. by Mr. Lemuel 
Hayward. The left side of this cranidium is very well preserved, but 
the right side is broken and the broken piece partially thrust under the 
glabella. Furrow 3 is distorted. 
As paratypes I have selected specimens Nos. 17, and 18, both of 
which are illustrated. All are in the M. C. Z. 
Measurements. Hoioryrre.— Cranidium 35 mm. long; glabella 
31 mm. long, 23 mm. wide at front of eyes; chord of palpebral lobe 
13 mm. long; rim 2 mm. wide at front of glabella, 4 mm. wide at corner 
of cranidium. 
ParatyPes.— No. 17. Cranidium 32 mm. long; glabella 30 mm. 
long, 22 mm. wide at front of eyes. 
No. 18. Cranidium and eleven thoracic segments, 76 mm. long as 
it stands, but as some segments are pushed under the head, the actual 
length was probably about 80 mm.; width of axial lobe at 2d segment 
20 mm.; total width of thorax, not including terminal spines, 58 mm. 
