CHITON. 409 



with smoke-black, and not unfrequently painted with lon- 

 gitudinal linear markings of the same hue upon the central 

 areas. In certain examples, and especially in those from 

 Scotland, the surface is wholly or partially concealed by a 

 black incrustation ; frequently, too, a slight coating of this 

 substance imparts a band-like effect to the posterior half of 

 each plate ; and sometimes probably this tint may be 

 regarded as the permanent colour of the shell, although in 

 the majority of specimens it is plainly superficial. In the 

 more elevated variety, the lateral triangles are more raised, 

 and the mucro of the hinder valve is more sharply pro- 

 minent. 



Mr. Lowe remarks that the plates are destitute of mar- 

 ginal teeth, but have their inner edges crenulated or 

 granular. Although several of our specimens exceed half 

 an inch in length and one third of an inch in breadth, we 

 regard these dimensions as the full average. 



The soft parts of the animal are of a somewhat tawny 

 flesh-colour. The hood of the head is rather thick mar- 

 gined. The branchial cordons are rather broad, and do 

 not extend on each side to half the length of the body. 

 There are about ten branchial leaflets on each side. The 

 space between the foot and the corner edges of the mantle 

 on each side is rather broad. The lingual dentition has 

 been described and figured by Lov^n ; the axile denticle 

 is widened out at the base, and remarkably contracted and 

 narrow in the centre ; the large uncinated black tipped 

 lateral teeth are very unequally denticulated at their in- 

 ward extremities. 



This species is as common and abundant below the 

 laminarian zone as cinereus is above ; perhaps even more 

 so, for we can scarcely dredge anywhere on our coasts 

 without taking it adhering usually to dead or living shells. 



VOL. II. 3 G 



