THE BRITISH FOSSIL BRACHIOPODA. 



389 



Paleozoic 



106 genera. 



Mesozoic 



34 genera. 



f"8 in Cambrian (Lower, of Sedgwick) 



67 in Silurian (Lower and Upper, of Mur- 

 chison). 



52 in Devonian 



40 in Carboniferous 



1 20 in Permian 



"~| Of these 106 genera, 11 passed from 

 the Palaeozoic into the Mesozoic, 

 40 became, as far as we at pre- 

 sent know, extinct during the 

 Silurian period, 27 passed into 

 the Devonian. 



r 1 5 in the Triassic "^ _ „ , _ . , „ ,. 



Of these 34 genera, 16 are peculiar 

 I 13 in the Rhsetic ! ... '.. , „ 



I 



Cainozoic and Re- 

 cent. 



21 genera. 



13 in the Rhsetic 



19 in the Jurassic... 

 18 in the Cretaceous. 



13 in the Tertiary .... 



20 in the Recent .... 



to the Mesozoic, 

 the Cainozoic. 



ed from 



Of these 21 genera, 12 passed from 

 the Tertiary into the Recent 

 period. 



Of course the above numbers must be taken as strictly provisional, for some 

 palaeontologists would admit a larger number of genera than I have done. Still, the 

 general inductions would not, I think, be materially altered. Of the 34 genera of 

 Lyopomata or Tretenterata 31 occur in the Palaeozoic rocks. Of these, 24 appear to have 

 become extinct during the Silurian period, 6 only being represented during the 

 Mesozoic and Cainozoic periods, 4 only during the Recent period. 



Of the Arthropomata or Clistenterata 76 genera are represented during the 

 Palaeozoic period, 37 in the Mesozoic, Cainozoic, and Recent periods. These details 

 will be better understood by a glance at the tables on pages 351 and 353 — 357. 



Dr. Waagen writes me that in the Third Part of his ' Monograph on the Salt-Range 

 Brachiopoda,' now in the press, he states that the classification of the Arthropomata or 

 Clistenterata, he thinks, should commence with Orthis, as it is the oldest genus of the 

 division at present known ; and he has drawn up the following scheme, which he 

 believes might perhaps serve as a base of a more rational classification of the Brachiopoda, 

 although he confesses that it is quite of a provisional nature. This scheme seems 

 to him to express the approximating affinities that exist among the greater part of the 

 Arthropomata. 



Pentamerinae. 



Porambonitidae. 



Atrypidae. 

 Rhynchonellidae. 



I 



(Enteletes). 



Orthis. 



Athyridae. 



Terebratulidae. 



Leptoccelia 

 (Tropidoleptus) . 



Productus. 



Strophomenidae. 



The subject will, however, demand much further consideration, for the passage 

 between the loop-bearing Terebratulidce and the spiral-bearing Spiri/erida has not yet 



