90 PLIOCENE MOLLUSCA. 



of boreal and even arctic species, as in the case of some of the Buccintims now to 

 be described. This might at first sight seem antagonistic to the zonal arrangement 

 I have adopted ; the difficulty is, however, more apj)arent than real. Counting 

 shells rather than species, such forms are exceedingly rare. I hope to deal with 

 this point more fully later on. The advance of the Scandinavian ice over the bed 

 of the North Sea would probably have driven many northern forms southwards, 

 while their invasion of the Crag basin at the Oakley stage may have been due to 

 a sudden breach in the land barrier which during the earlier part of the Crag 

 history seems to have separated it from northern seas. 



Buccinum undatum, Linne, 1758. 



1758. Buccinum undaium, Liune, Syst. Nat., ed. x, p. 740, uo. 410. 



1848. Buccinum undatum (type), S. V. Wood, Mou. Crag Moll., pt. i, p. 35, tab. iii, fig. 12 c. 



1853. Buccinum undatum, Forbes and Hauley, Brit. Moll., vol. iii, p. 401, pi. cix, fig. 5. 



1867. Buccinum, undatum, Jeffreys, Brit. Couch., vol. iv, p. 285, pi. Ixxxii, fig. 2. 



Remarlcs. — The typical form of this British and northern species, a strong 

 shell with coarse sculpture and prominent ribs as shown in the works named 

 above, is not very common in the English Crag, although some of the varieties 

 described below are fairly so. They are not adequately represented in our public 

 collections, as such fossils are difficult to obtain in perfect condition. Unfor- 

 tunately collectors have paid but little attention to fragmentary specimens, though 

 they are often of great interest and importance. Many such specimens have been 

 thrown away as useless which might have been identified by careful examination. 



Of the recognised forms of this shell several were described and figured by 

 Wood, but there are others more or less abundant in our deposits which deserve 

 notice. A number of Buccinums, moreover, generally regarded as distinct, have 

 turned up in the Crag during recent years or have remained unnoticed in our 

 Museums ^ ; the latter are usually labelled B. undatum, probably under the 

 impression that most of our Crag specimens might be considered varieties of that 

 species. 



Var. clathrata, S. V. Wood. Plate VI, figs. 1, 2. 



1853. Buccinum undatum, Forbes and Hanley, Brit. Conch., vol. iii, pi. cix, fig. 3. 

 1872. Buccinum undatum, var. clathratum, S. V. Wood, Mou. Crag Moll., 1st Suppl., p. 18, tab. ii, 

 fig. 3. 



Uemarlcs. — This form, agreeing generally with one of the figures given by 



1 Such forms, however, have not been wholly unnoticed. Some years ago Mr. A. Bell reported to 

 me the discovery of the northern species, B. groenlandicum aud B. terrx-novx in the Newbournian 

 and Butleyan Crags. 



