TURRITELLA COMMUNIS. Ill 



Pleistocene: Middle glacial sands : Billockby, Clippesby, Hopton. Bridlington. 

 Selsey, Nar Valley, March gravels, Blackpool, Kelsey Hill and many other glacial 

 and post-glacial deposits in Great Britain and Ireland. 



Upper Pliocene : Italy, Sicily, Holland. 



Pleistocene: Italy, Sicily, Christiania Tapes-banks (Br0gger),Trondhjem (0yen). 



Remarks. — As stated above, I am disposed to regard the recent T. communis as 

 specifically distinct from the extinct and fossil T. tricarinata of the earlier zones of 

 the Crag and of the Mediterranean deposits. This view has not been generally 

 accepted, and some confusion has arisen in consequence. Whatever we call them, 

 whether varieties of one species or by different specific names, they are not the 

 same, having a zonal value which, from a stratigraphical point of view, is important 

 and should not be lost sight of. 



The one, T. trioarinata, is a comparatively old form, going back, according to 

 Prof. Sacco, to Miocene times, ranging upwards through the Italian Pliocene to 

 the Pleistocene of Sicily and Calabria, but not recorded as now living in the Medi- 

 terranean or elsewhere ; similarly, although it is exceedingly common in the Coral- 

 line and Waltonian horizons of the Crag, it gradually disappeared from the later 

 zones and is not found in our Pleistocene beds. 



On the other hand, I have no note of the occurrence of T. communis in the 

 Coralline or Waltonian Crag, and it was unknown from them to Wood, Jeffreys, 

 the brothers Bell, and C. Reid. It was not until the latest or Icenian stage of the 

 Crag that it began to establish itself in any abundance in the East Anglian area, 

 but in the British Pleistocene it became one of the most common and characteristic 

 fossils. 



T. tricarinata, moreover, was a southern form which died out in the Crag basin 

 as the climate became colder, pari passu with the arrival in it of the northern and 

 arctic mollusca. T. communis, on the contrary, has a range comparatively northern, 

 living on the Norwegian coast as far north as the Lofoten Islands and in Iceland, 

 flourishing in these latitudes under the glacial and subglacial conditions of the 

 Pleistocene epoch. Prof. Br#gger reports it from the post-glacial beds of the 

 Christiania fiord, and Dr. 0yen from those of Trondhjem. 



It may be interesting to notice that while it has not been found at St. Erth, it 

 occurs rather plentifully in the newer western deposits of Wexford and the Isle 

 of Man. The spiral sculpture of specimens from Wexford and from our Pleistocene 

 deposits is generally coarser than that of the recent British shell ; see also Br^rgger, 

 op. cit., pi. ix, fig. 9. 



Such facts illustrate the importance of the careful study of varieties, or of 

 supposed varieties, which may sometimes lead to results of considerable interest. 



Jeffreys employed Linne's specific name of terebra for the present shell, but 

 MM. Bucquoy, Dautzenberg and Dollfus point out that his Turbo terebra was a 

 species from the China seas (op. cit., p. 225). 



