46 ME. E. S. C0BB0ED ON TWO SPECIES OF [March 1913, 



Bohemian specimens, but are not mentioned in the description. 

 Rather stronger rugosities are seen on the anterior border itself, 

 and these creep over the margin on to the doublure in their course 

 towards the facial suture. 



The area of the free cheek (PI. IV, fig. 7) is flat and wide, its 

 lateral border is gently but decidedly convex, and parallel with it 

 there is a slight rise in the surface forming the incipient intra- 

 marginal ridge, which I have not seen indicated in any of the 

 figures of the Bohemian specimens. 



The pleurae (PI. IV, figs. 13 & 14) have a rather narrow groove, 

 terminating subcentrally in the anterior portion of the thorax 

 (fig. 13) and close to the posterior margin in the more posterior 

 segments (fig. 14). The point, which is directed strongly backwards, 

 is connected with the body of the pleura by a bold curve, and 

 is decidedly slender. In Barrande's figures (pp. cit. pi. x) the points 

 are much wider. 



The pygidia figured here (PL IV, figs. 15 & 16) are rather 

 small ; but, on comparison with Barrande's figure of the complete 

 trilobite, are not smaller than might be expected to accompany the 

 smaller cranidia (figs. 8 As 9). They both show a more quadrate 

 outline than the Bohemian specimens, and have only two transverse 

 furrows on the axis instead of three. Fig. 16 shows an approach 

 to an oval form, but has fairly straight sides. 



The hypostoma (Pi. IV, fig. 17) seems to be quite the same as 

 the Bohemian form. 



Test. — Apart from the rugosities already mentioned, the surface 

 is smooth. 



Comparison with the Allied Species. 



In P. tessini Brongniart the front of the glabella is pointed, the 

 glabellar furrows, though curved, are more direct ; the length of 

 the eye-lobe is less than a third of that of the head-shield ; the 

 posterior branch of the facial suture is relatively longer and inclined 

 at a more acute angle to the margin ; the pygidium is distinctly 

 spatulate, being wider behind than in front, and it has three or four 

 furrows across the axial lobe ; the curve joining the body of the 

 pleura to its point is of comparatively short radius. The Shrop- 

 shire form approaches P. tessini in having -the points of the pleura 

 slender. 



In P. Iwrlani Green the front of the glabella is well rounded ; 

 the glabellar furrows are nearly direct ; the length of the eye-lobe 

 is less than a third of that of the head-shield ; the facial suture 

 behind the eye is relatively longer, and inclined more acutely to the 

 margin ; the pygidium is almost circular, and has but one furrow 

 across the axial lobe ; the pleural points are comparatively wide ; 

 and there is a tubercle on the occipital ring. 



The cranidium of P. abenacus Matthew has a general form very 

 similar to that of the Shropshire variety ; the eye-lobe is as large 

 •or larger ; the glabella is truncately rounded in front, and traversed 



