198 balanidjE. 



only alluding to the less frequent points of difference, and then sepa- 

 rately describe the more marked varieties. 



(leneral Appearance. — Shape of shell generally tubulo-conical, or 

 conical, or globulo-conical, rarely depressed. Orifice either large and 

 rounded-trigonal, or small and oval, either entire or less frequently 

 toothed. Surface quite smooth, or longitudinally ribbed; ribs of 

 variable strength, not unfrequently flexuous or branching, sometimes 

 roughened with blunt or sharp projecting, irregular points, or more 

 rarely with almost cylindrical, upturned, long spines ; the simple 

 longitudinal ribs are generally most strongly marked in young speci- 

 mens. Colour, generally varying from pink, to pink tinged with 

 purple, to dark, inky purple, more or less striped, longitudinally, with 

 white or pale tints; rarely the shell is of the brightest rose-colour, 

 either uniform or longitudinally striped ; sometimes it is pale purplish, 

 or dark blue ; and sometimes dark chocolate-purple : the ribs, when 



sent, are generally more or less white, sometimes snow-white. That 

 there is much variation in colour, and in the prominence of the longi- 

 tudinal ribs, is quite certain, as the two sides of the same individual 

 sometimes differ greatly in these respects. The radii are generally 

 rather darker coloured than theparietes, but sometimes they are lighter, 

 even in the darkest tinged specimens. The surfaces of the radii are 

 occasionally finely plaited in lines parallel to the basis. In some infre- 

 quent varieties the radii have oblique summits, making the orifice of the 

 shell to be toothed. The sheath is generally feebly coloured, but 

 sometimes bright chesnut-brown, and sometimes blueish. 'The strength 

 of the shell varies considerably; some of the globulo-conical varieties 

 are extremely massive. Size; basal diameter of largest specimen very 

 nearly three inches; height of the highest specimen three inches. 



Young specimens are apt to have a peculiar aspect ; for their shell 

 is often strongly ribbed longitudinally, and the summits of their radii 

 are sometimes oblique. Their scuta are sometimes deeply pitted in 

 radiating lines. Their colours are generally pale. I have seen speci- 

 mens attached to kelp from the Cape of Good Hope, with their parietes 

 white and ribbed, and their radii mottled with pinkish-purple; I have 

 seen other young specimens from the Galapagos Archipelago, of a 

 uniform greyish-blue. 



The Scuta generally have their lines of growth moderately prominent ; 

 occasionally they are longitudinally striated, with the lines of growth 

 fiexuous and upturned at intervals into small, sharp, hood-liked pro- 

 jections, which are symmetrically arranged in straight lines radiating 

 from the apex of the valve ; I have seen this structure in some speci- 

 mens of var. crispatus and in var.occator (PI. 2, fig. 1 b) ; and I have 

 noticed an intermediate state in var. communis. The degree to which 

 the basi-tergal corner of the valve is rounded off varies much even in 

 var. communis (PI. 2, fig. 1 a, 1 d, 1 e). The articular ridge (1 c, 1 e) 

 is broad and much rerlexed ; and often, but not always, distinctly 

 hooked (1/). The adductor ridge is confluent with the articular ridge, 

 and runs straight down the valve, bounding the cavity for the depressor 

 muscle ; generally the adductor ridge is blunt, and so little prominent 

 as barely to deserve notice; but I have seen it sharp and prominent in 



