PRELIMINARY CLASSIFICATION OF TRILOBITES. 



I have here given chiefly British genera as examples. There are, of course, many others. 

 It is evident that the lowest and most rudimentary group of all is that of the 

 Agnostidce, which, therefore, may be at once placed at the base ; and there is not likely to 

 be much difference of opinion as to the place of the Phacopiclce, as the typical and most 

 perfect group of the order. The other genera fall more or less naturally into an inter- 

 mediate place, but are developed along two distinct lines, as follows : 



A.— Trilobites with facial su- 1. PHACOPID^. 



ture ending on the ex- Pliacops. Trimerocephalus. 



ternal margin. Eyes well Acaste. Chasmops. 



developed, usually fa- Odontochile. 

 cetted externally. (Pha- Cryphoeus. 



copini.) 2. CHEIRURIDiE. 



Cheirurus. Staurocephalus. ? Cybele. 

 Sphserexoehus. Deiphon. ? Encrinurus. 

 Amphion. 1 Zethus. 



B.— Facial suture ending on 3. ACIDASPID-32. 



the posterior margin. 

 Eyes (usually) mode- 

 rately developed, smooth. 

 (Asaphini.) 



7. CALYMENIDJE. 



Calymene. 

 Homalonotus. 



Acidaspis, &c. 



4. LICHADJE. 



Lichas. 



5. CYPHASPIDJE. 



Cyphaspis. 

 Aulacopleura, &c. 



8. CONOCEPHALIDiE. 6. HARPEDIDiE. 



Conocoryphe. Sao. Harpes. 



Solenopleura. ? Centropleura. 

 Holocephalina. 



12. PROETIDJE. 



Brachymetopus. GrifBthides. 

 Phillipsia. Proetus. 



Phaeton. 



11. BRONTEID^E. 



Bronteus. 



Angelina. 



10. ASAPHIDiE. 



Illsenus. Nileus. 

 Stygina. Isotelus. 



Asaphus. 

 Ogygia. 

 Barrandia. 



Basilicus. 



Niobe. 

 Psilocephalus. 



\ 



% \ 



9£ ?» 



9. OLENIDJE. Remopleurides. 

 Olenus. Triarthrus. 



Sphserophthalmus. Tiresias. 



Paradoxides. Cyphoniscus. 



Anopolenus. Hydrocephalus. 



^Efflina. 



C, — Facial sutures obscure, or 

 submarginal, or none. 

 Eyes often absent. (Am- 

 pycini). 



13. TRINUCLEIDJE. 



Dionide. Trinucleus. 



Ampyx. 





D. — Without eyes or 

 facial suture. 

 (Agnostini.) 



14. AGNOSTIDjE. 



Agnostus. 

 Trinodus. 



■a 



£ o^ 



March, 1864. 



J. W. S. 



