PENGELLT — FOSSILS OF DEVON AND CORNWALL. 
15 
' Catalogue,' the Heteropodous Mollusca are, in Table I., included in 
the class Gasteropoda. 
It is scarcely necessary to remark that the fossils of Devon and 
Cornwall do not fully represent the organisms of the Devonian age, 
as seven other classes — Pisces, Pteropoda, Cirrepedia, and Annelida, 
amongst animals, and Cellulares, Monocotyledones, and Polycotyle- 
doues amongst plants — have been found in rocks of this age else- 
where ; and of these the two first and the fifth have been met with 
in other British localities. The reptiles Steganolepis and Telerpeion, 
of the Elgin Sandstone, are not enumerated here, as some doubt 
attaches to the question of their chronology, if indeed they are not 
certainly Triassic. The single articulated class, Crustacea, is by no 
means rich in any way ; with one exception, all its genera are Tri- 
lobites, and commonly contain but one species each. The most 
important class numerically is Brachiopoda, to which one hundred 
and eight species belong, that is, thirty-one per cent, of the entire 
series. The families and genera of Cephalopoda are richer in species 
than those of any other class, averaging sixteen for each family, and 
ten for each genus. 
The most striking fact in this connection is the specific abundance 
of Brachiopoda and Cephalopoda, and the paucity of the classes 
Lamellibranchiata and Gasteropoda, as compared with the numerical 
rank of the same classes in the existing Fauna. This fact will, 
perhaps, be most strikingly exhibited by the following table, which 
has been thus computed: in the left-hand column the aggregate 
number of the species of fossil mollusca found in Devon and Corn- 
wall has been put = one thousand, and the numbers belonging to 
each class computed to this ; the right-hand column has been formed 
on the same principle, and is based on the data given by Forbes and 
Hanley in their ' History of British Mollusca.' 
TABLE II. 
Devonian Mollusca of 
Devon and 
Existing British 
Cornwall. 
Mollusca. 
42 
72 
410-5 
15-5 
186 
359-5 
179 
521-5 
182-5 
31-5 
1,000 
1,000 
It appears, then, that within existing British seas the Lamelli- 
branchiates are about twenty-four times more numerous specifically, 
than the Bracliiopods, whilst within, what may be called, the same 
area, the latter weie to the former, during the Devonian period, 
