NORMAN: ON THE M0LLU3CA OF BERGEN FIORDS. 47 



loS. Saxicava rugosa, (Lin.) Living specimens found are 

 small; but at Bukken fossil valves of enormous size and 

 thickness are washed out of a deposit on the shore, together 

 with Mya truncata var. Uddevalensis^ &c. These valves 

 correspond with those figured by Middendorff from the 

 Siberian Seas {Saxicava p/wladis, Middendorff Siberische 

 Reise, Band, ii. (185 1), p. 253, pi. xxiv.,fig. 1—7). 



no. Dentalium entalis, Lin. 



111. Dentalium entalis var. striolatunn, Stimps. 



Dentalium striolaiuni, Stimpson. Proc. Boston Nat. Hist. 

 Soc, Oct. 1851 ; Shells of New England, 1851, p. 28. 



Dentalium abyssorum, M. Sars. Foss. Dyrelevninger fra 

 Quartasrperioden, 1865, p. 42, pi. iii., fig. 100—106. 



Dentalium abyssorum^ Jeffreys. Brit. Conchol., iii., p. 197, 

 pi. ci., fig. I. 



112. Dentalium abyssorum var. agile, M. Sars. 



Dejitalium incertum, Philippi. Fauna Molluscorum regni 

 utriusque Sicilise, ii., p. 207 (fide Jeffreys, but notZ>. incertum, 

 Deshayes). 



Dentalium agile, M. Sars. G. O. Sars' "Remarkable 

 forms of Animal Life from the great Deeps off the Norwegian 

 Coast," i. (1872), p. 31, pi. iii., fig. 4—15. 



Lcannot satisfy myself that the differences which separate 

 Dentalium abyssorum and D. agile of Sars from D. entalis, are 

 anything more than varietal, though doubtless many other 

 so called species of Dentalium have been established on 

 similarly slight modifications. D. abyssorum appears to be a 

 deep-water, striated form of D. entalis, to which it is united 

 by every step in gradation of the amount of sculpture, so that 

 it is impossible anywhere to draw a positive line of distinction; 

 nor can the D. agile of Sars be regarded, I think, as other 

 than a deep-sea, slender, straighter form of the same species. 

 As we descend further into the abyss of the sea, where the 



