394 



GENERAL SUMMARY TO 



r Pebidian. 

 Pre-Cambrian ■] Arvonian. 



*» Dimetian. 



Laurentian Laurentian or Lewisian gneiss. 



Of British Tretenterata we have 15 genera and about 125 species. 



Tertiary 



2 



genera and 



3 species. 



Cretaceous 



2 



,, 



c „ 



Jurassic 



3 



,, 



27 „ 



Rhaetic 



1 



t) 



1 „ 



Permian 



2 



}) 



3 „ 



Carboniferous 



3 



}J 



12 „ 



Devonian 



3 



,, 



G „ 



Silurian 



15 



„ 



71 „ 



Of British Clistenterata we have 



59 genera, 



named varieties. 









Tertiary 



5 



genera and 



7 species. 



Cretaceous 



12 



,, 



81 „ 



Jurassic 



11 



„ 



214 „ 



Permian 



9 



,, 



16 „ 



Carboniferous 17 



,, 



141 „ 



Devonian 



30 



,, 



128 „ 



Silurian 



28 



,, 



195 „ 



genera, about 762 species, and about 80 



Table showing the approximate number of British species in each geological 



tretenterata. 



Lingula, Bruguiere. One species only seems to pass from the Car- 

 boniferous into the Permian ; one (Z. squamiformis = L. mold) 

 passes from the Devonian into the Carboniferous 



Lingulella, Salter. All Cambrian and Silurian 



Dinobolus, Hall. All Silurian 



? Obolus, Eichwald. 4 species, doubtfully referred to Eichwald's 

 genus. Probably different. All Silurian 



Obolella, Billings. All Silurian 



Kutorgina, Billings. Silurian only 



Discina, Lamarck. One passes from the Devonian into the Carboni- 

 ferous 



Paterula, Barrande. Silurian only 



Trematis, Sharpe. 3 species, all Silurian 



Acrothele, Linnarsson. Silurian 



Orbiculoidea, d'Orbigny. Silurian 



Crania, Retzius. All apparently characteristic of their formation ... 



Pholidops, Hall. Silurian 



Acrotreta, Kutorga. Silurian 



Siphonotreta, Kutorga. Silurian 



