124 BRACHIOPODA. 



Ordovician the Brachiopods are much more numerous 

 than in the Cambrian, and they attain their maximum in 

 the Silurian, their decline begins with the Devonian and 

 becomes especially marked in the Mesozoic. The most 

 important genera in the Cambrian are Lingula, Obolella, 

 Discina, and Orthis (the last being the only representative 

 of the Articulata) ; in the Ordovician, Lingidella, Obolella, 

 Orthis, Strophomena, Leptcena ; in the Silurian, Lingula, 

 Atrypa, Orthis, Meristella, Rhynchonella, Pentamerus, 

 Strophomena, Chonetes ; in the Devonian, Uncites, Stringo- 

 cephalus, Atrypa, Orthis, Spirifer ; in the Carboniferous, 

 Chonetes, Athyris, Spirifer, Productus, Terebratula, Rhyn- 

 chonella; in the Permian, Productus, Spirifer, Rhynchonella. 

 The majority of the Palaeozoic genera die out before the 

 commencement of the Mesozoic, the most important 

 genera now being Terebratula, Terebratulina, Waldheimia, 

 Rhynchonella, and Crania. In the Tertiary the Brachio- 

 pods are rare, the chief forms being Terebratula, Wald- 

 heimia, and Rhynchonella. 



