CYPRINA. 445 



that he takes it among the Orkneys in all depths, and quite 

 as large in seven as in forty fathoms. We have gathered 

 it exposed alive at very low tides in the Frith of Forth. 

 On the Irish coast it inhabits the northern, eastern, and 

 southern shores, occurring on the first in from five to 

 twenty-five fathoms (Thompson) ; and on the last as deep 

 as sixty (M'Andrew). 



The peculiarities of its distribution are very interesting, 

 as this is one of the Mollusca common to European and 

 North American seas, and a member of the faunas of all 

 the crags. The remarkably wide bathymetrical range of so 

 large a shell indicates a capacity for enduring many changes 

 of conditions which illustrates strikingly the cause of its 

 great geographical and geological extension. A species so 

 constituted must be expected to present considerable varia- 

 tions, and we cannot admit the separation of its fossil re- 

 presentatives into distinct specific types, as has been done 

 by Professor Agassiz, on account of slight variations in the 

 degrees of their tumidity. Every British sea-going col- 

 lector knows how variable living specimens are in this re- 

 spect. Even Agassiz himself, however, though he endea- 

 voured with earnest good-will to draw a line between the 

 fossil specimens from the Clyde glacial beds and living ex- 

 amples, could not do it. The hair was too fine to split. 

 During the glacial epoch this and a few other boreal Mol- 

 lusks had extended their range to the Mediterranean, 

 whence they have long disappeared, though their remains 

 are preserved in the upheaved newer pliocene strata of 

 Sicily. 



