found on the coast of Northumberland and of Durham. 337 



highly probable that I should be induced to regard these and 

 pelagicum as so many forms of the deep-water or Coral zone va- 

 riety : in this case the earlier name of Fabricius would have to be 

 used instead of mine. 



But depth is not the only element inducive of a varietal 

 difference : the nature of the sea-bottom, whether hard or soft, 

 as is well known to fishermen and many naturalists, exercises a 

 marked influence in this respect. In my paper, as it was read 

 at the Southampton Meeting of the British Association, another 

 variety was described under the name of crassumy and which I 

 am disposed to think is represented by the shell figured in 

 Pennant's ' British Zoology,' pi. 73. One of the principal dif- 

 ferences between it and B. magnum is in the general absence 

 of an epidermis, which, when present, has somewhat the ap- 

 pearance of network, or it assumes the character usual in litto- 

 rale : moreover, it is a thicker, narrower and smaller shell ; the 

 whorls are more angulated and more numerous, the aperture is 

 considerably smaller, the canal is narrower, the waves are closer 

 together, more rugose and more angulated, occasionally showing 

 a tendency to become biplicated on the middle of the whorls ; the 

 cords are thicker and closer to each other, and the intervening 

 furrows are narrower, rarely having more than one or two threads. 

 Notwithstanding these differences, I have seen specimens which 

 it was difficult to say whether they belonged to B. crassum or 

 B. magnum. The colour of this variety is generally reddish 

 brown externally, and yellowish white internally; occasionally 

 the outside of the shell is marked with dark brown bands on a 

 light-coloured ground. My largest specimen, which has nine 

 whorls, is 3|^ inches long and 2 broad. I possess an interesting 

 specimen (one of the doubtful forms just alluded to) 5 inches 

 long and 2J broad, and having nine whorls : the first seven 

 whorls have all the characters general to crassum ; while the last 

 two are covered with an epidermis, and, in other respects, agree 

 with those of magnum : I look on this specimen as having been 

 a crassum for so long of its existence, and afterwards, perhaps 

 through migrating to soft ground, to have become changed into 

 a magnum ! The variety crassum is common on hard ground in 

 the Laminarian and Coralline zones on the coasts of Northumber- 

 land and Durham, where it ranges from seven to thirty fathoms : 

 it also occurs on the Yorkshire coast ; but I apprehend it will be 

 a scarce shell further south, where soft ground is prevalent. I 

 am not yet sufficiently acquainted with rock-inhabiting forms 

 from deeper water, including the Coral zone : from what has 

 passed under my observation, however, I am induced to believe 

 that they approximate more or less to magnum and pelagicum. 



Ann. ^ Mag. N. Hist. Vol.xix. 24 



