position of the palpebral lobe, and shortens the movable cheek. Not 

 only is the cephalic limb of the Harlani much wider than that of the 

 spinosus, but it presents other and very characteristic diiferences- In- 

 stead of its lateral portion reaching to about the seventh pleura, and 

 almost touching their tips, it only reaches to the fourth pleura, and is 

 quite a distance from the body. 



I have already spoken of the position of the palpebral lobe and the 

 shortness of the cheek in the Harlani The palpebral lobe is also 

 shorter and much less convex than in the spinosus. We also observe 

 a slight difference in the posterior lobe of the cheek, which is broad 

 at its tip and narrows gradually towards the dorsal furrow. 



The axis of the body narrows much more towards the pygidium in 

 Harlani, than it does in the sjmwsiis. The jDleurse also present 

 marked differences, which I think M. Barrande would not have failed 

 to notice if he had possessed other means of comparison than 

 photographs. The external, or curved portion of the pleurae, is much 

 longer in comparison to the internal portion in the Harlani than in 

 the spinosus, the curve being so long that they do not present that 

 somewhat angulated appearance which we often notice in that species. 

 In fact, they much more resemble the pleuraB of Paradoxides imperi- 

 alism and would be more easily mistaken for them than for those of 

 P. spinosus. This comparison of the pleurte holds through all of them. 

 In the middle segments of the body the curved portion of the pleurse 

 is fully equal to the horizontal portion, and as we descend towards the 

 pygidium the difference becomes much more marked, the pleursB as- 

 suming a long sweeping curve almost from the point of their attach- 

 ment to the axis. So that the posterior pleurae, especially, are very 

 different from what they are either in the long or wide form of the 

 spinosus, for according to the figures of M. Barrande they appear to 

 differ in the two forms. Another very interesting feature of the 

 pleurse is, that in the smallest specimen of the Harlani which I have 

 seen, the last pleura extends to a very marked distance beyond the 

 pygidium. According to the description of M. Barrande this only 

 occurs in the largest specimens of the spinosus. 



The pygidium I have not found sufficiently well preserved to make 

 an accurate comparison of the two species. 



I have found several specimens of the hypostome well preserved, 

 and these add to the evidence of their belonging to a species distinct 

 from the spinosus. They have the anterior portion much wider than 

 in the spinosus, so that that part presents a much longer oval. 



I have now reviewed some of the principal points of difference 

 which I have noticed in comparing the specimens from Braintree with 

 the Paradoxides spinosus, and after carefully weighing their value I 

 am fully convinced that the Paradoxides Harlani is really a distinct 

 species, so related to the former that without doubt it was a represen- 

 tative of that species in the Primordial fauna of America. 



