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(sect, a), balanus nigrescens. 211 



There can be no doubt that this species is the B. nigrescens 

 in Chenu, who had access to Lamarck's original specimens ; 

 and there can be equally little doubt that it is the B. gigas 

 of Ranzani, collected, during Baudin's expedition, at King- 

 George's Sound : it is essentially allied to B. psittaciis, but 

 in external appearance strikingly resembles some of the 

 varieties of B. tintinnabulum. 



General Appearance. — Shape tubulo- conical : walls smooth, some- 

 times longitudinally ribbed : colour ashy-grey tinged with blue, but 

 many specimens are dark purplish-blue, owing to the disintegration of 

 the outer lamina, and consequent exposure of the almost solidly filled 

 up, dark blueish parietal tubes ; on the other hand, some specimens 

 are quite white. Ranzani describes the colour as earthy-violet, which 

 is very characteristic of some of the specimens. The orifice is apt to 

 be rather small, compared to the size of the specimens, and tends to be 

 hexagonal. The radii are often rather narrow. The opercular valves 

 are tinted pale blue. The basal diameter of the largest specimen is 

 two inches, and its height two and a quarter. 



The Scuta have their basi-tergal corner much rounded off', as in 

 B. psittacus, so that the tergal margin does not extend more than half 

 down the valve. The surface is somewhat prominent, along a line 

 runing from the apex to the point of chief curvature in the basal 

 margin. The surface is not striated. Internally, the articular ridge 

 is little prominent, and not reflexed ; the lower end depends as a free, 

 sharp style or point. The adductor ridge is moderately sharp, and 

 stands some little way distant from the articular ridge : it is produced 

 downwards, and forms a moderately deep and large cavity for the de- 

 pressor muscle ; but this cavity is not closed, and does not extend up, 

 as in the two last species, to the apex of the valve. 



Terga, narrow, with a sharp, prominent, needle-like beak. Spur, 

 long, narrow, placed at less than its own width from the basi-scutal 

 angle: the basal margin on both sides slopes down to the spur: the 

 scutal margin is not inflected. Internally, the articular ridge is very 

 feebly developed, but extends down close to the basi-scutal angle. On 

 the under surface in the upper part of the valve, there is a short, very 

 slight ridge, extending on the carinal side, near and parallel to the 

 articular ridge ; this slight ridge plays an important part, as in the 

 two foregoing species, in the formation of the beak or apex. Crests 

 for the depressor muscle are hardly distinguishable. 



The Walls appear to vary in some degree in strength and thickness ; 

 as is likewise the case with the opercular valves. In some of the 

 thinner specimens, the parietal tubes are large, and the longitudinal 

 septa are furnished with small, sharp denticula. The tubes are often 

 thickly lined or almost filled up solidly with blue shell ; they are not 

 crossed by transverse septa. 



The Radii vary in width ; externally they are often finely ribbed 

 transversely, at other times they are smooth ; their septa are fine and 



