22 



THE GEOLOGIST. 



The fifty-six genera thus limited are generally poor in species, the 

 aggregate number belonging to them being no more than ninety-two ; 

 that is, fifty-eight per cent, of all the genera contain no more than 

 twenty-six per cent, of the total number of species. Torty-one of 

 these fifty-six genera contain each but a single species in the British 

 Devonian deposits. The only genera thus limited that can be said to 

 be rich in species are Stromatopora, Acervularia, and Clymenia. The 

 first, a genus of Amorphozoons, contains five species, all limited to 

 South Devon ; the second, a group of corals belonging to the great 

 Palaeozoic family CyathopJiyllidw, contains fi"\ e species, all peculiar to 

 South Devon ; and the last, a genus of Cephalopod mollusks belonging 

 to the family NautilidcB, contains eleven species, all found at South 

 Petherwin, not one being met with elsewhere in Britain. With the 

 single exception of Cyrtoceras rusticum, found at South Petherwin — 

 and this probably a synonym for OrtTioceras arcuatum — the genus 

 Cyrtoceras is restricted to South Devon, where it is represented by 

 twelve species. 



The distribution of the ninety-seven genera of fossils found in the 

 two counties is exhibited in the following table :- — 



TABLE V. 









Peculiae 



TO 





Totals. 





» 



























fl 



ft 









P 



ft 













m 





d 





d 



oi 





d 





d 





o 



h4 





















Amorphozoa 



4 



3 

 14 











4 





1 







Zoophyta 



20 











20 



"i 



4 



'i 



3 



Echinodermata 



6 



2 







3 





3 





1 



4 



1 



Crustacea 



8 



6 









"i 



7 





1 



1 



2 





7 



3 







"i 





5 



i 





3 



2 



Brachiopoda 



Laniellibraucliiata . . . 



16 

 17 



6 

 5 







3 



i 



16 

 11 



4 

 2 



i 



8 

 8 



7 

 7 





14 



7 











13 







7 



6 





5 













4 







2 



5 





97 



46 







7 





83 



1 « 



8 



34 



33 











56 





97 





41 







Every genus of the classes Amorpliozoa, Zoopliyta, and Brachiopoda 

 occurs iu South Devon, and with the exception of Cephalopoda it 

 contains a greater number of genera in each class than either of 

 the other areas. All the genera of Cephalopoda appear at South 

 Petherwin. 



