somewhat more than as two to one; that is, they were then fifty times more abundant than at present in comparison with the other great class of Acephala. In like manner it is seen that, relatively to the Gasteropoda, the Cephalopoda were, in this early age of our planet, seventeen times more numerous than now. It may be added that, within the district under notice, the registered species of Devonian Brachiopoda absolutely, and in a high ratio, exceed those belonging to the same classes within existing British seas; and the fact is the same for the world at large.
The five columns of Table I., headed "Peculiar to," and distinguished by the initials of the five areas respectively, show the number of fossil species which, so far as England is concerned, are peculiar to each; from which it appears that the fossils of Devon and Cornwall have a very limited and unequal distribution. Two hundred and ninety-seven species, that is, eighty-five per cent, of the whole, are peculiar to one or other of the areas, whilst no more than fifty species, or scarcely fifteen per cent, of the entire series, are distributed amongst them. Lower South Devon monopolizes no fewer than one hundred and ninety-one species in this way, or, in other words, fully sixty-four per cent, of the two hundred and ninety-seven, species thus limited, or fifty-five per cent, of all the known Devonians of the two counties are restricted to this single area. Lower North Devon, on the other hand, appears to be equally remarkable for its fossil poverty.
It is unnecessary to say that five areas taken two, three, four, and five together are capable of making twenty-six different combinations, namely, ten two together, ten three together, five four together, and one five together. The ten combinations, however, headed "Common to," in Table I., are all that are required to show the distribution of the fifty species not confined to one single area. Not a single species of this ancient Fauna is common to the five areas, and only one, the coral Cyathophyllum celticum, is found in each of four of them. The well-known coral Favosites cervicornis is the only fossil found in each of the three contemporary deposits of Lower South and North Devon and Cornwall. Of two areas only. Upper North Devon and Upper Cornwall have the greatest, and Lower South Devon and Lower Cornwall the least, number in common; in the former a total of seventeen, and in the latter of eight species only. Dissimilar as are the organic distributions in these two pairs of areas, they are probably just what might have been expected. In each pair the two areas are pretty closely connected geographically, and are supposed to be contemporary, as their names imply; but in the former the mineral character is much the same in each area, and we have a greater organic similarity than ordinary; in the latter the deposits are very unlike—Lower South Devon being rich in limestone as well as slate, whilst in Lower Cornwall the fossiliferous beds are all but exclusively argillaceous—and there are very few organic remains in common; a marked instance, probably, of the influence of the mineral character of the ancient sea-bottom on organic existence. Though
