122 G. F. MATTHEW : ILLUSTRATIONS OF 



The species is exceeded iu length, aud, as has already been observed, in size also, by 

 some examples of Asuphus megistos. 



3. — Affinities of the Species. 



Head-Shield. — In considering the affinities of this species, it is evident, for many 

 reasons, that we shall need to look among the large trilobites, with shortened eyelobes. 

 Among these are several which, like P. regina, are marked by a broad glabella, with rather 

 short posterior lobes, aud a narrow occipital ring, and by having the eye set well back, so 

 that the anterior extension of the dorsal suture exceeds the posterior in length. These 

 species are P. Bennettii, P. Harlani and P. Forchamrneri, and they are mostly marked by a 

 broad axis in the thorax, and by pleurse of comparatively uniform length, with tips that 

 are more or less foliaceous. In these respects they differ widely from the other group 

 of great Paradoxides, including P. Tessini, P. Bohemicus and P. Davidis, which are remarkable 

 for the advanced position of the eye, and the narrow thorax with spinous tips to its 

 pleurse. In the extraordinary width of the cephalic shield, uo Paradoxides equals the 

 great Acadian species, in which the length is to the width as 1 to 2| ; in P. BenneUii it is 

 1 to 2^, in P. Forchamrneri it is the same, and in P. Temni-genuinns it is asl to 2J. This 

 unusual width is due largely to the great expansion of the folded margin of the moveable 

 cheek. 



Free Cheek. — The feature in P. regina, which strikes the observer as being uniisual, is 

 the enormous width of the marginal fold of the free cheek. This is only parallelled in P. 

 BenneUii, though P. Forchamrneri also has a wide, marginal fold ; and a cheek from South 

 Braintree, Mass., which Mr. Walcott refers to P. Harlani, is very similar to the free cheek 

 of our species, but differs in the genal spine, which is very much longer than that of 

 P. regina. In the shortness of the geual spine, no other of the great Paradoxides except 

 p. Bennettii approaches our species, and this also resembles our species in the backward 

 prolongation of the free cheek ; in the Newfoundland trilobite, however, this feature is 

 abnormal, and the exaggerated backward extension of the cheeks is spoken of by Mr. 

 Salter as a " lappet-like lobe." 



Thorax. — The thorax of our species is remarkable for the great width of the axis, and 

 for the rapid tapering of the last four rings ; in these features it reminds one of P. Tessini 

 genuinus, referred to in the historical outline on a preceding page. Its broad axis also brings 

 it into relation with P. Bennettii, but that species, if we are to be guided by Mr. Salter's 

 figure, was macro-pleural, since he represents the second pleura as longer than its fellows, 

 while, iu our species, there is no such extension ; nevertheless, the wide, leaf-like pleurae, 

 of the Acadian species, are only paralleled among the large trilobites, by the similar parts 

 iu P. Bennettii. Unfortunately, we have not the posterior segments of this last species, aud 

 so do not know how they compare with those of P. regina, but we do observe a point of 

 resemblance here with the corresponding parts of the P. Harlani : iu both of these species, 

 the three last segments of the thorax have shortened pleurœ, and in this differ markedly 

 from the P. Te,sstrt« group of the larger Paradoxides ; but we do not find entire uniformity 

 between the two American species in respect of this abbreviation of the three last pleurœ, 

 for, while in P. Harlani they are progressively shorter toward the pygidinm, in P. regina 

 they are progressively extended, as the series is traced toward the same part. Among the 



