402 Prof. F. M'Coy on the Classification of 



1. Harpes (Gold.). 



?2. Harpidella (M'Coy). See below. 



?3. Amphion* (Pand.). 



5tli Subfam. Agnostin^. 



Minute, blind ; only two thoracic segments ; bead and abdomen 

 covered by nearly equal and similar rotundato-quadrate shields. 



This subfamily includes both the families Phalacromides and 

 Battoides of Hawle and Corda, distinguished solely by the ser- 

 ration or smoothness of the margin of the tail, — a point in my 

 mind of generic value at most. 



Prom tiie absence of eyes, and the very slight powers of loco- 

 motion argued by so small a number of thoracic, feet-bearing, 

 rings, it occurs to me that the Agnostin^ may hold the same 

 position among the Trilobites that the Suctoria do among the 

 Crustacea generally; that group being similarly distinguished from 

 its allies by the want of eyes, few body-rings, little or no powers 

 of locomotion, and abnormally and variously shaped bodies; 

 being parasitic generally on fish. Bophyrv,s, the analogous group 

 among the Isopod Crustacea, is always parasitic on the gills of 

 the larger Crustacea, under their carapace ; and such I strongly 

 suspect were the habits and mode of life of the Agnosti, living in 

 all probability attached to the gill-feet on the under side of Tri- 

 lobites, some of the largest known species of which accompany 

 those little animals. 



1. TRiNODUsf (M'Coy)= Arthrorachis (Hawle and Corda). 



2. Agnostus (? British). 



Subgen. 1. Diplorhina { (H. & C). 



* This genus and Encrinurus present some points of analogy, and may 

 serve to indicate the passage from this subfamily to the Paradoxinte by 

 meaife of Zetfius, but I unfortunately cannot refer to any specimens of the 

 body-rings of either Amphion or Encrinurus at present, and have therefore 

 some uncertainty about them. I may here remark on the great apparent 

 inequality of extent or numerical value of the five gi'oups into which I have 

 distributed the great family of Trilobites, that it results chiefly from a pecu- 

 liarity of geographical distribution, and in great measure disappears when 

 the large number of recently described foreign genera are included : thus 

 the Harpedina; and Paradoxincs, which seem so meagrely represented in the 

 above list of British genera, acquire a prodigious development in the Silurian 

 rocks of Bohemia. 



f I originally defined this genus in 1846 in ray * Synopsis of the Silurian 

 Fossils of Ireland,' and pointed out its differences from Agnostus ; subse- 

 quently Hawle and Corda have figured and described the group under the 

 title of Arthrorachis in their * Prodrom.' on Bohemian Trilobites, without 

 knowledge of what I had done, also pointing out its obvious differences from 

 Agnostus (or Battus). 



X 1 have noticed the Diplorhina triplicata in the black Llandeilo shale of 

 Builth. 



