POLYCH^TA— BENHAM. 37 



In one case the belly is nearly as deeply pigmented blue as the dorsum; but 

 this is very exceptional, as the ventral surface is generally without pigm.ent. 



There seems to be no very definite correlation between the colom-ation and the 

 depth at which the worms were found, for in sorting out the specimens from the jars 

 in which they reached me, I rather naturally separated out those in which the colours 

 were strikingly dift'erent, under the impression that I had to deal with distinct species. 

 Thus, in one lot from 25 fathoms, I find fom- different plans of colouration or, as I sup- 

 posed, four different species. 



Nevertheless, after talnilating the worms under their colours and their depths, 

 it seems tha<' there is a rough correlation between them. Thus, in shallow water, 

 from the shore line down to 60 fathoms, the general tone of colour of the elytra is darker 

 and variegated in brown, while the dorsum is without pigment, or has pale trans- 

 verse lines of brown. The elytra, too, are more firmly attached to the elytrophores 

 than in other cases. 



But in those worms that come from greater depths, say, 110-400 fathoms, the 

 elytra are paler and more uniformly coloured, and may even be colourless and trans- 

 lucent; and they are readily deciduous. On the other hand, the dorsum is now 

 pigmented more deeply or more extensively, and it is from these depths that the 

 handsome dark blue and violet worms were obtained. But this applies only to the 

 larger specimens. 



The smaller worms are apparently less afiected by depth ; or it may be that 

 the change in the amount of pigment is a measure of age, for in a general way the smaller 

 individuals are deeply colouretl, while the larger ones, above 60 mm. in length, have 

 pale or colom'less elytra, with a more deeply pigmented dorsum. The smaller worms, 

 from 10-30 nun. are generally found in less deep water than those from 40-90 mm. 



The texture and ornamentation also of the elytra present considerable range of 

 variation, for in some the surface appears under a lens to be smooth, whereas in the 

 more typical forms there is a row of pale conical tubercles along the posterior border, 

 as shown in Willey's figm-e 2, pi. XLI. These are usually better developed on the 

 elytra from the hinder region of the body, while the more anterior ones may be without 

 them. Again the entire surface may be covered with small cones, visible under a lens, 

 and giving them a rough appearance to the naked eye. The marginal fringe may be 

 present or absent. 



The prostomium is usually white, whether the dorsum of the body is pigmented 

 or not, but in one case at least, it is marked transversely by a narrow band of brownish 

 pigment (as in var. lagiscoides, as figured by Gravier (1911), pi. VI, fig. 64). The 

 peristomial cirri, anal cirri, and dorsal cirri are browmish. 



In spite of these variations in colour there are two features in the distribiition 

 of pigment that appear to be constant, namely :— (1) the dark greyish-blue tint on the 



