168 BUCCINUM. 



or less deeply sculptured, two kinds may usually be distinguished, 

 a large and a small kind, those of the latter being by far the more 

 numerous, and distributed upon the surface of the others. These 

 kinds we shall call, for convenience, the primary and secondary 

 grooves, or ridges, as the case may be. The difference between 

 them is very conspicuous in B. glaciale. The columella has 

 normally three folds, an upper, middle, and lower one ; the lower 

 one constituting the oblique inferior margin of the columella. 

 These folds are not always distinct, but all of them may be made 

 out in B. tenue. The middle fold is obsolete in most of the 

 species, but is very prominent and tooth-like in B. ciliatum. The 

 layers of the shell are very distinct in this genus, the outer coat 

 being most frequently of a brownish color. - The periostracum is 

 generally ciliated with minute processes along the lines of growth, 

 corresponding to their intersections with the secondary ridges. 



The operculum is oval or subcircular, and may have the nucleus 

 near the centre, or more or less approximated to the posterior 

 (outer) margin, according to the species. On the lingual ribbon, 

 as in all the Buccinidse, we find three teeth in each row, the 

 central one of which is lamelliform, with denticles on its poster- 

 ior edge ; while each lateral tooth has two strong hook-shaped 

 denticles, with smaller ones between them. The denticles of the 

 central tooth are more numerous than in Neptunea. 



With one or two doubtful exceptions, the genus Buccinum is 

 restricted geographically to the temperate and frigid seas of the 

 northern hemisphere. More careful examination, both of the 

 shell and soft parts of the Antarctic species referred to the genus, 

 is required, before deciding upon their actual pertinence to it.* 



Geologically, the history of the genus commences in the Plio- 

 cene formation. They are found in the European tertiary 

 deposits of that age, even as far south as the shores of the Medi- 

 terranean. They become very numerous in the Pleistocene 

 deposits, both of Europe and North America, but reach their 

 maximum development in the existing seas. 



The shells of the genus Buccinum are peculiarly liable to 



* The Antarctic as well as tropical species described as Buccinum all 

 belong to other genera; the genus is limited to northern seas. G. W. T,, Jr. 



