PE5GELLT FOSSILS OF DEYOK AXD COR>'WALL. 
28 
The genera found in the two counties were not all confined to the 
Devonian period. The following table shows their Chronological dis- 
tribution so far as the Silurian, Devonian, and Carboniferous deposits 
of Britain are concerned. 
TABLE VI. 
e3 
Common to 
a 
1* 
lian G* 
Devon 
T3 
»§ 
S « 
§ 
as 
3 . 
3 
II 
ifero 
man 
an. 
ifero 
nian 
Q 
a 0 u 
c 0 
1 
evoi 
0 >_3 
0 
JO » 
Amorphozoa 
4 
3 
1 
Zoophyta 
20 
10 
5 
'3 
"'2 
Echiiiodermata 
6 
2 
3 
1 
Crustacea 
8 
1 
5 
2 
Bryozoa 
5 
2 
Bracbi )poda 
1^ 
"3 
"2 
8 
3 
LamtU brauchiata . . . 
17 
2 
1 
9 
5 
Gasteropoda 
14 
2 
11 
1 
Cephalopoda 
5 
1 
2 
2 
Totals 
97 
24 
14 
41 
18 
From which it appears that twenty-four genera, — about one-fourth 
of the whole series,— are peculiar to Devonian deposits, fourteen 
common and restricted to the Silurian and Devonian, forty-one com- 
mon to all three, and eighteen common and restricted to the Devonian 
and Carboniferous; hence a total of fifty-five Devonian genera occur 
in the preceding, and fifty-nine in the succeeding period. Some of 
the genera occur in oS'eozoic deposits, and a few in the existing 
Fauna. 
AVhen the numbers of species contrtined in each of the forty-one 
genera of tlie fourth column (Table VI.) are tabulated in parallel 
columns for the three periods, the figures present themselves in four 
different principal forms of succession, as may be illustrated by taking 
the genera Favosites, Cyathophyllum^ Loxonema, and Ortlioceras. 
Sil. Dev. Carb. 
Favosites 8 5 la descending-despending series. 
Cyathoi)hylluin 9 14 8 ascending-descending. 
Loxoneina 2 8 14 ascending-ascending. 
Orlhoceras 55 12 35 descending-a:5cending. 
The first kind shows that the maximum specific development occurs 
in the Silurian era, the second in the Devonian, and the third in the 
Carboniferous ; the fourth kind may perhaps be regarded as a sort 
