416 VENERIDiK. 



or four simple or interrupted, lighter or darker, broader or 

 narrower-coloured rays, on a very pale or whitish ground ; 

 sometimes but two remarkably broad orange-brown rays, 

 which are occasionally more or less distinctly edged with 

 very small linear markings of a darker hue. More 

 rarely the entire surface is of an uniform white, but where 

 colour is present at all, the rays seem always more or 

 less developed, though frequently only composed of con- 

 fluent linear markings. A kind of obscure reticulation, 

 formed by short and crowded minute coloured lines, or 

 small dots, is very prevalent, especially in specimens from 

 Guernsey and the Avarmer jjortions of our coast : where 

 this pattern is peculiarly distinct, the rays are usually of a 

 dark roseate-brown, and the general effect of colouring 

 remarkably rich. 



The great alteration of the sculpture with age has been 

 the cause of the immature state being regarded as a distinct 

 species. In its most typical stage the surface is covered 

 with not very numerous broad and but little elevated obtuse 

 belts, separated by shallow and much narrower smooth in- 

 terstices. The fry have only crowded and rather depress- 

 ed fine concentric costella? ; in the earlier stages concentric 

 recurved lamina often arise, which, gradually becoming 

 solid with age, form laminar belts which are solid and 

 shelving below, but hollow and recurved above : at these 

 periods the interstices are at least as broad as the eleva- 

 tions, usually diminishing in width as age advances. 



In certain examples the hinder dorsal slope is coarsely 

 dentated, as it were, by the projection and abrupt termina- 

 tion of the laminar belts ; this does not take place, how- 

 ever, in the full-grown shells, where the belts at once 

 diminish in elevation at the posterior extremity. The 

 ventral margin is always more or less arcuated, rises grejitly 



