280 BALANID^E. 



latter owing to the persistent epidermis ; the bands are pale, and often 

 fade away in the lower, and sometimes in other parts of the shell ; the 

 epidermis is generally more persistent on the narrow rounded radii 

 than on the parietes, and hence the radii are generally yellowish. The 

 opercular valves are pale dull purple : the sheath is darker purple, 

 with the exception of the portions of the alee added during the diametric 

 growth, which are of a dead white, and are externally conspicuous. 

 The scuta are striated longitudinally. I may remark, that, excepting 

 the narrowness of the radii, with their quite smooth, rounded and very 

 oblique summits, some specimens are hardly distinguishable, in external 

 aspect, from varieties of B. amphitrite. If the specimens from the 

 north-east coast of Australia, of which I have seen many (but unfor- 

 tunately only one small one had its opercular valves), form, as I fully 

 believe, merely a variety; it is characterised by its nearly uniform 

 beautiful rosy pink, without any distinct longitudinal bands : of these 

 specimens I have seen one two inches in basal diameter, and three in 

 height: of ordinary duller-coloured striped specimens, the largest waR 

 1*7 in basal diameter. Of the perfectly white var. (b), I have seen 

 several specimens, the largest being '6 of an inch in diameter: these 

 have a somewhat peculiar aspect, but I have met with only one speci- 

 men with opercular valves, and that was extremely young : I at first 

 considered this form as specifically distinct ; but I can point out, 

 after careful examination of the whole shell, operculum, and internal 

 animal of the young specimen, no sufficient diagnostic characters. 



Scutum, plainly striated longitudinally, with the striae dividing the 

 prominent lines of growth into squarish beads : internally, the upper 

 part of the valve is roughened : the articular ridge is short, remarkably 

 little prominent, and not refiexed ; the adductor ridge is blunt and 

 little prominent ; sometimes it is almost confluent with the articular 

 ridge : there is a deep but variable depression for the lateral depressor 

 muscle ; and in young specimens of var. (a) it was almost absent. 

 Tergum: the surface exhibits traces of longitudinal striae: there is 

 a deep longitudinal furrow, with the sides folded in and quite closed 

 in full grown specimens : the scutal margin is considerably curved 

 towards the scutum. The spur is long and narrow, with the end 

 bluntly pointed, placed at rather above its own width from the basi- 

 scutal angle; the basal margin slopes but little towards the spur: the 

 crests for the depressores are feebly developed. 



Parietes : their internal surfaces are strongly ribbed longitudinally, 

 with the basal ends of the ribs coarsely denticulated, and with the 

 denticuli extending close to the outer lamina. The radii are generally 

 narrow, but their width varies ; their summits are very oblique, 

 smooth, rounded, and inflected, with the lines of growth, in the 

 uppermost part, curving inwards ; their sutural edges, in the upper 

 inflected portion, are quite smooth, without septa ; in the lower and 

 larger portion, the edge is crenated with excessively fine teeth or septa, 

 not denticulated : the radii, like the parietes, have no inner lamina : 

 the recipient grooves in the opposed compartments are smooth, and 

 are in the lower part of the shell of unusual depth. The alee, diffe- 

 rently from the radii, generally have their summits very slightly 



