v.] INTRODUCTION. XCVll 



which have been taken on the bank) have not^ so far as 

 I am aware, ever been detected in any of our Tertiary 

 strata. The two other Arctic species (Nalica clausa 

 and Trophon Scalay^iformis) inhabit the upper coasts of 

 Norway, as well as more northern seas. The first-named 

 species has a range, according to M ^Andrew and Barrett, 

 from the shore to 150 fathoms. It occurs in the Eed 

 Crag, as well as in almost every pleistocene bed which 

 has been examined in this country ; and I noticed it in 

 the collection of Dr. Van Geuns at Utrecht, among some 

 shells which he had found in the Subapennine deposit 

 of Palermo. This species is not included in Philippi's 

 list of Sicilian fossils. The distribution of the other 

 species appears to have been equally extensive; and I 

 have a fresh specimen, recently inhabited by a hermit 

 crab, which was dredged fr-om deep water oflP the Aber- 

 deen coast and obligingly presented to me by the late 

 Professor Macgillivray. It is quite possible that a plei- 

 stocene bed may have formerly existed in the spot which 

 is now occupied by the Tui-bot bank, and that the con- 

 tents of this bed may, by the action of the tide or marine 

 currents, have become mixed up with the existing pro- 

 ducts of the adjacent sea-bed ; and the appearance of 

 some of the shells to which I have refen^ed might 

 warrant such a conclusion. But, inasmuch as many 

 relics of the Glacial epoch, such as Leda pygmaa and 

 Area raridentata, still survive in a few and widely sepa- 

 rated parts of that extensive area which was once sub- 

 ject to Arctic conditions, it will not be surprising if all 

 the species I have thus mentioned as doubtful inha- 

 bitants of our seas should also have lingered on in their 

 old quarters and be really British. The conjecture that 

 these shells may have been accidentally transported by 

 sul^marine currents from the Arctic Sea to the Irish 



