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. Forty- one of 
these fift^'-six genera contain each but a single species in the British 
Deyonian deposits. The only genera thus limited that can be said to 
be rich in species are Stromatopora, AcervuJaria, and Clymenia. The 
first, a genus of Amorphozoons, contains fiye species, all limited to 
South Devon; the second, a group of corals belonging to the great 
Palaeozoic family CyathophylUdce, contains fi^e species, all peculiar to 
South Deyon ; and the last, a genus of Cephalopod mollusks belonging 
to the family NautilidcB, contains eleyen 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 Orthoceras 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. 
Peculiab 
TO 
Totals. 
■< 
M 
H 
o 
pi 
Q 
P 
ft 
< 
d 
^' 
d 
m 
d 
)^ 
d 
o 
EH 
1-4 
'A 
& 
D 
Amorphozoa 
4 
3 
4 
1 
"i 
Zoophyta 
20 
14 
20 
4 
3 
Echinoderraata 
6 
2 
3 
3 
1 
4 
1 
Crustacea 
8 
6 
1 
7 
1 
1 
2 
7 
3 
6 
"l 
5 
16 
i 
3 
2 
Brachiopoda 
16 
i 
4 
i 
8 
7 
Laniellibranchiata . . . 
17 
5 
3 
11 
2 
8 
7 
Gasteropoda 
14 
7 
i 
13 
7 
6 
Cephalopoda 
5 
4 
2 
5 
97 
46 
7 
3 
83 
8 
8 
34 
33 
56 
97 
41 
Every genus of the classes Amorphozoa, Zoophyta, and Brachiopoda 
occurs in 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; 
