EVOLUTION. 



317 



LOWER CAMBRIAN 



MIDDLE CAMBRIAN 



UPPER CAMBRIAN 



WimanellaO" 



-o 



,(y 



Eostrophomena 

 Eoorthis 



'-0 



^-,FHTkehT- 

 ~\J burgia 



Billingse| 



aQ_ 



OrusiaO- 



^/'o'tusiaO 

 Billings'ella ,''' 



"O Eoorthis 

 Finkeln- /-\ 

 burgia ^ 



Billingsella 



O 



' Jamesella 



a- 



/ Nisusia,0- 



Wynnia'O 

 Jamesella 



-o 



— o 



Protorthis 



-QJamesella 



Protorthis 



o 



/ ^'--O Swan- 

 / y" ^ tonia 



-o 



S ynti'ophia 



OLoperia 



Syntrophia 



Huenella 



O 



-O Syntrophia 

 OCIarkella 



Q Kutorgina 



-Q Schuchertina 



'a 



I phidella 



Iphidella p . 



Helmersenia .Q 



MickwitziaO 

 pMcromitra 



Micrortiitra ,'' 



OVolborthia 



-o^ 



Paterina 



o 





_Ry Stella 



O 



,--o- 



'-0- 



Elkania 

 _— -'-O 



,,0 Neobolus 



O Fordinia 



o 



ODicellomus 

 Elkania 



O C-QBroggeria 



'O 



Schmidtiai 



Curticia^O/'' / 

 Obolus ,-'''/'' /',/ 



O 



O^ 



Mickwitzella" 

 Westonia 



O Acritis 



-O Obolus 

 )--QLingu- 



lobolus 

 "O Westonia 



\ DelgadellaQ 



X Lingulella y 



^O Paleeobolus 

 Lingulella 



Lingulella 



^O 



Lingulepis 



"~~, __Lepternbolon_ 

 Lingulepis 



<)~- 



O Lingulella 

 Lingula^ 



"O Lingulepis 



— OQuebecia 

 ^ Botsfordia 



;0^ 



-O 



O- 



,0 Schizopholis 

 -OBotsfordia 

 O Discinolepis 



ORedlichella 

 .,-'' Acrothele 



Acrothele 



AcrotretaXD; 



Linnarssonella 



o 



DiscinopsisQ 

 Acrotreta 



Linnarssonella 



O Acrothele 



o 



^ 



Trematobolus 



^'-p^ Acrothyra ^ 

 Orbiculoidea 



^ o^ 



Trema- ^ APhilhe- 



'O 



K:t. o^ 



YorkiaO 



tobolus^^~v ^^ dra 



Dearbornia'O 



' nizariiuun ^ 

 _ K.?y??J'l'J!!gL^/S-. 



Siphonotr_e_t_a_ 



Figure 18.— Schematic diagram of evolution of Cambrian Brachiopoda. 



