542 Prof. H. H. Swinnerton — Classification of Trilobites. 



Their predominant peculiarity, viz. the intersection of the facial 

 suture with the margin at the genal angle, is evidently an inherent 

 tendency in the Ptychoparian constitution, for it manifests itself in 

 Triarthrus. 



He. 



&% 

 ■— o 



w £■ 



o & 



2 B 

 P o 



as TO 

 S to 



15 



SS MESOiYACIDAEi- 



Progressive Stages. 



MJcropygous.. 



Heferopygoua. Isopy^ous 



WiHiouf free Cheeks. 



WM tree Cheekb (may be losF Secondarily.) 



Proropana. 



-^Marellidae. 



-Bemopleuridae.. 

 - Paradoxidae. 



-Zacanfhoidae. 



-OLENIDAE.U.sM- 



'--Orycfoceplialidae. 



---, — C0N0CORVPHIO/1E: — ■ 



/Solenopleundae. 



,_-' Oikellocepbalidae.— 



■PTVCHOPARIDAE.:— 



\ s ^ — Bafliyuridae. — i 



\ '■ c - - --/Isaphidae: — ■ 



n "< i — Illaenldae 



-Cslpuraenidaei— i 

 N Homalonoridae • 



_ i Trinucleidae.- 



■ -Harpedidae. 



■ Raphiophoridoe. 



" It- Ellipsocephjlidae 1 



■ •— Aeglinidae— 

 --?Sliumardiida«. 



-Odonfopleundae. > 



1 : Li c h a <d I d a e . . 



■— Bfonreidaer-' 



. >— Encnnur/clac - 



-Cheiruciclae- 



-Phacopldac. 



Burlingidae. 



1 /Ignosrirtae. 



H 

 zn 



r - 



o 



CD 



H 



> 



o I Qrrler PEOTOFABIA. , 



Raymond 1 rightly emphasizes the very primitive condition of the 

 Middle Cambrian Asaphid Ogt/giopsis, and traces from it the main 



1 Trans. Eoy. Soc. Canada, ser. in, vol. v, p. 116, 1911. 



