Page:A Treatise on Geology, volume 1.djvu/190

 174 existing (e. g. nucula, lingula, isocardia); but others are quite different, (as pleurorhynchus, producta, euomphalus, goniatites, &c.), and seem to belong to another order of creation. About 60 per cent, of the species belong to extinct genera; and it is very remarkable, that brachiopodous bivalves, which, in existing nature, are perhaps to other shells as 10 in 1000, were in these ancient periods as 10 in 34. The goniatites are most beautiful and characteristic features of this system, being found in none of the more recent strata.

Crustacea existed during the accumulation of these rocks, but bore little resemblance to the present forms of the class: the trilobites of these rocks are, however, less numerous and varied than in the older Silurian rocks, where they are remarkably plentiful.

Annelida have left many as yet undescribed remains on the surfaces of the flagstones in the millstone grit and limestone series. Some are enough like Nereis to be referred to the wandering setigerous tribes.

The fishes of the carboniferous system (Burdiehouse, Leeds, Bradford, Manchester, Bristol, Wales,