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., pi. 8, fig. Id). 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. 

 harlani, 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. Ha;\Ties has seventeen thoracic 

 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. 



Types. — As the holotj'pe of this species I have selected cranidium 

 No. 16 (Plate, fig. 1) recently presented to theM. 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 o% 

 which are illustrated. All are in the M. C. Z. 



Measuremejits. Holotype. — 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. 



