Robert O. Bell — Notes on Pliocene Beds. 557 



The shells of Fusus antiquus found in the lower beds of the 

 deposit at Walton are invtiriably sinistral ; but in the middle zones of 

 the Eed Crag about Sutton the dextral shell occurs plentifully, and 

 both forms are often carinated ; but in the upper horizon in the 

 neighbourhood of Butley, and in the Norwich Crags, these carinations 

 are more pronounced, and the reversed shells generally fewer. It is 

 here that the Boreal and Arctic Mollusca are most numerous, and 

 that the number and size of shells having southern affinities dwindle 

 into smaller proportions. 



The contention of Mr. Searles Wood that this species first appeared 

 in the reversed state, afterwards becoming dextral in the course of 

 time, certainly appears to agree with known facts. In the grey 

 sand at Walton, as in the Belgian equivalents of this zone, no dextral 

 forms have been found, although in the upper Bed Crag at this section 

 two broken and worn specimens have rewarded a long continued 

 search. 



How to account for this important variation of form is more 

 problematical : is it dependent on alteration of climate ? Perhaps 

 the gradually cooling condition of the Crag seas was prejudicial to 

 the original state of the shell, the dextral variety may be a hardier 

 form gradually superseding the other, until it has become the rare 

 exception only occasionally found. The cold seas of the Arctic 

 climate certainly possess two Molluscs, Buccinum deforme, Midd., 

 and B. Harpa, Morch. (HeUotropis, Dall.), which are always sinistral, 

 and Middendorf mentions the reversed F. antiquus as found in the 

 Polar Sea and Eussian Lapland, and Woodward as from the Sea of 

 Ochotsk ; but these examples must be extremely rare, and altogether 

 it seems that the sinistral condition of any of the shells of Mollusca, 

 whether that condition be normal or not, is much less frequent in 

 cold than in warm or even temperate seas. In Great Britain it is 

 doubtful whether the reversed Fusus has been found living anywhere 

 except in the neighbourhood of the German Ocean, where among 

 many thousands of others an example closely approaching the 

 Walton type is occasionally seen ; but in Vigo Bay, in the north of 

 Spain, a small colony still lingers, the late Mr. McAndrew having 

 collected it with a number of other shells of Celtic character. The 

 specimens do not seem to differ materially from other coarsely 

 striated forms, and are certainly identical with those from the 

 Pleistocene deposits of Sicily ; but there is no certain authority for 

 its existence in the Mediterranean. 



The small reversed form from the Wexford gravels may be men- 

 tioned here ; it is different from any other known to the writer, 

 being very thick and quite smooth ; it is said to be associated with 

 many southern shells. So little, however, is accurately known with 

 regard to the position or contents of the various beds of marine 

 gravels in Ireland, that at present any conclusions must be premature. 



The variet}'^ of form and sculpture exhibited by this species in the 

 Eed Crag is more than equalled by its divergence in modern times. 

 The Fusi found in the Northern Hemisphere no doubt present great 

 differences, but in their general characters most of them have a 



