244 BALANID.E. 



pinkish or dark purple approximate stripes, which often become con- 

 fluent ; in one group, the whole shell being thus uniformly coloured, 

 without any vestige of stripes. I have seen another group from an 

 unknown locality, in which the lower part of the shell was uniformly 

 blueish-grey. A variety from Australia has narrow approximate dark 

 claret-coloured stripes, transversely freckled with white. Lastly, in 

 the variety cirratus, the whole shell is very pale purplish-brown, with 

 indistinct longitudinal brownish stripes, transversely freckled with white 

 lines. I considered this as a distinct species, until quite lately finding 

 forms which I could not possibly determine whether to class as 

 B. cirratus or amphitrite. 



The radii are generally snow-white, or freckled with a bright 

 mahogany tint, or rarely clouded with purple, or in the pink varieties 

 with pink. The scuta are dull purple or pink, generally with a white 

 band along their tergal margin ; often, however, they are white, with 

 merely one or two purple fasciae. The thickness or strength of the 

 shells varies much ; some specimens attached to a floating cane, from 

 Natal and the Philippine Archipelago, were extremely strong ; others, 

 from the Mediterranean and Australia, and some tubular varieties from 

 the West Indies, were very thin, translucent, and fragile. Size : large 

 specimens generally attain a diameter of from half to three quarters of 

 an inch in basal diameter ; and I have seen one or two specimens an 

 inch in diameter. 



Scutum; sometimes the surface is very smooth, but generally the 

 growth-ridges are moderately prominent; the latter are occasionally 

 very finely beaded, and this seems always the case with var. cirratus. 

 Internally, the articular ridge is prominent and reflexed : the adductor 

 ridge is sharp, very prominent, and straight ; it runs parallel to the 

 occludent margin ; close to its lower side there is often a depression 

 (PI. 5, fig. 2i), sometimes bounded by a slight ridge, as if for the at- 

 tachment of a muscle, but there certainly is no muscle here : rarely 

 the adductor ridge is only slightly prominent : there is a small and 

 shallow little pit of variable depth for the lateral depressor muscle. 



Tergum (2 k — 2 o) ; this valve is here far more variable than in any 

 other species : in the commonest purple-striped forms (2 /), the 

 valve is rather broad, the basal margin lies in nearly a straight line on 

 the opposite sides of the spur, which is placed at rather less than its 

 own width from the basi-scutal angle ; the spur is rather short, and in 

 width about one fourth of the entire valve ; its lower' end is either 

 bluntly pointed or more commonly nearly square (2 A) and parallel to 

 the basal margin : in young specimens it is generally sharper than in 

 older ones. Externally, in the line of the spur, there is either a slight 

 longitudinal depression, or more rarely a deep furrow. The carinal mar- 

 gin is more or less convex, and is formed by upturned lines of growth: 

 the scutal margin is broadly inflected. Internally, the articular ridge 

 in the upper part is very prominent : the crests for the tergal depressor 

 muscle are moderately prominent, but very variable. Sometimes the 

 carinal portion of the basal margin is slightly hollowed out. In var. 

 Stutsburi (2 m, 2 n, 2 o), and in some white varieties, which differ most 

 in the shape of the tergum from the commoner varieties, the whole 



