510 TROCHID^. 



shell. There are neither tubercles, creiise, nor any peculiar 

 sculpture upon it ; the anterior portion is, however, thick- 

 ened by a more or less distinct linear callosity. The 

 outer lip is simple and acute ; the pillar is straight, narrow, 

 not much rounded nor dilated, and succeeded by a faint 

 concavity. Ordinary specimens do not exceed two-fifths 

 of an inch in length, and a third of an inch in breadth. 



Certain of the Mediterranean examples differ so widely 

 at first sight from the variety which inhabits our own 

 shores, as scarcely to be recognisable for the same species. 

 In the typical or first described form, the whorls are a 

 little swollen at the sutures, and the surface both above 

 and below is radiated with continuous wavy and obliquely 

 flexuous lines of black, that are often double upon the body- 

 volution. In the produced variety the colouring has gene- 

 rally an articulated arrangement, the whorls are narrower 

 and longer, and as well as the base, which is destitute of 

 the ordinary angulation, much more rounded. 



This shell is, as a British species, confined to our southern 

 shores. It inhabits the laminarian zone, living on the 

 leaves of Zostera, as at Herm and Torbay (S. H.), 

 Guernsey (Barlee) ; Exmouth (Clark) ; on the Devon- 

 shire and Cornish coasts ; common at Falmouth (Alder) ; 

 in fifteen fathoms ofi" the Land's End (M'Andrew) ; coast 

 of Cork and Bantry Bay (Humphreys) ; Baltimore harbour 

 (Allman). 



It does not occur to the north of Britain, but ranges 

 southwards to the Mediterranean. 



