rLA It It, 



Lower Cambrian Trilobites. 



^' '^ftr)?o^-/fw^lit7v^rfrn ^■- ,-^/'«^'''««'V'*: vcrmontana(nan); 3. ElUptoccplmla asaphoides Emmons; 4. C'aKfuVa 

 W^Tf'nff ^ T?;.^ a ■^' ^- ^^^i^o-f^-Jerulfi {Unnarsson); 6. TraH«n-(aira;cr/«a7i».s (Wanner); 7, 8. PaY/f«;»/a.s' traiisitans 

 r^V'ViH^.L K ^- *^^ ^/^ enlargement of the posterior portion of figure 7, showing the rudimentary segments and 

 p>gidium beneath the telsoulilie segment. 9. Olcncll us thompsoin Uall 



m^Virl 'I'ft.'^lJ.'J'lii'' principal genera of the Mesonacidse; shows changes from most primitive form Xevadia 

 lirfo^f il } ?^ °'^^1™J^ °^ descent, as represented byfigures 2, 3, and 7, to 0?c«rf?«.f (figure 9), also another 

 fisnre%tn^d n^ tTl?^ w^"-S' ^' ?i.^' ^',^Vi\6' probable line of descent 'from Xcvadia (figure' 1) to Holmia 

 (ngnie b) , ana on to I'aradoxides. (See pi. 17.) 



