Relation of the Fauna of the Crag to that of the recent Seas.—By far the greater number of the recent marine species occurring in the several Crag formations are still inhabitants of the British seas; but even these differ considerably in their relative abundance, some of the commonest of the Crag shells being now extremely scarce—as, for example, _Buccinum Dalei_—while others, rarely met with in a fossil state, are now very common, as _Murex erinaceus_ and _Cardium echinatum._ Some of the species also, the identity of which with the living would not be disputed by any conchologist, are nevertheless distinguishable as varieties, whether by slight deviations in form or a difference in average dimensions. Since Mr. Searles Wood first described the marine testacea of the Crags, the additions made to that fossil fauna have not been considerable, whereas we have made in the same period immense progress in our knowledge of the living testacea of the British and arctic seas, and of the Mediterranean. By this means the naturalist has been enabled to identify with existing species many forms previously supposed to be extinct. In the forthcoming supplement to the invaluable monograph communicated by Mr. Wood to the Palæontographical Society, in which he has completed his figures and descriptions of the British crag shells of every age, list will be found of all the fossil shells, of which a summary is given in the table, p. 202. To begin with the uppermost or Chillesford beds, it will be seen that about 9 per cent only are extinct, or not known as living, whereas in the Norwich, which succeeds in the descending order, seventeen in a hundred are extinct. Formerly, when the Norwich or Fluvio-marine Crag was spoken of, both these formations were included under the same head, for both at Bramerton and Thorpe, the chief localities where the Norwich Crag was studied, an overlying deposit occurs referable to the Chillesford age. If now the two were fused together as of old, their shells would, according to Mr. Wood, yield a percentage of fifteen in a hundred of species extinct or not known as living. NUMBER OF KNOWN SPECIES OF MARINE TESTACEA IN THE CRAG. CHILLESFORD AND ALDEBY BEDS Total number Not known as living Percentage of Shells not known as living Bivalves 61 4 9·5 Univalves 33 5 Brachiopods 0 0 NORWICH OR FLUVIO-MARINE CRAG Bivalves 61 10 17·5 Univalves 64 12 Brachiopods 1 0 RED CRAG _(Exclusive to many derivative shells)_ Bivalves 128 31 25·0 Univalves 127 33 Brachiopods 1 1 CORALLINE CRAG Bivalves 161 47 31·5 Univalves 184 60 Brachiopods 5 3