398 



Prof. F. M'Coy on the Classification of 



Faceted pleurce of Trilobites. 



a, Calymene ; b, Ellipsocephalus ; c, Asaphus ; d, Phacops; e, Odontochile ; 

 f Dysplanus ; g, Illsenus ; k, Forbesia ; i, Homalonotus ; k, Trimero- 

 cephalus. 



Non-faceted pleurce of Trilobites. 



/, Ogygia; m, Lichas; n, Bronteus ; o, Ampyx ; p, Harpes; q, Conocepha- 

 lus ; r, Paradoxides ; s, Zethus; t> Cryphagus ; w, Acidaspis; v, Stau- 

 rocephalus ; w, Olenus ; x, Trinucleus ; y> Ceraurus. 



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4. Harpedina; 5. Agnostinm. The British genera would arrange 

 themselves as follows, and where the value of any of the groups 

 was not previously settled, I have added a few explanatory words. 



1st Subfam. Asaphin^. 



Pleurae bent down at the ends, each with a distinct trigonal facet 



at the anterior edge. 



These are the most perfectly organized Trilobites ; they have 

 a compact ovate form, and from the deflexion of the margin are 

 of considerable depth ; they all, I believe, have the power of roll- 

 ing into a ball, and are the only Trilobites having the triangular 

 facets at the anterior edges of the ends of the pleurae. The fol- 

 lowing are British genera and subgenera : — 



Gen. 1. Phacops (in a wider sense than Emmerich). Lateral ce- 

 phalic angles prolonged backwards ; glabella wider in front 

 than at base ; sides with three large segmental furrows ; eyes 



