210 BALANID.E. 



corner not being so much rounded off*, and consequently in the arti- 

 cular ridge, which is rather more reflexed, descending in proportion 

 lower down the valve : the cavity at the basi-tergal corner is in propor- 

 tion broader. The valves in the two species differ, also, but only in 

 young specimens, in the occludent half being tinted, both externally 

 and internally, purple, whereas in B. psittacus the whole valve, at all 

 ages, is white. In the terga the spur is removed fully its own width 

 from the basi-scutal angle, whereas it is not half this distance in 

 B. p)sittacus. The scutal margin is here much more inflected. In 

 B. psittacus there is a remarkable patch of purple on the inside of the 

 valve, between the articular ridge and a second special ridge ; of this 

 purple patch there is here no trace, consequently the beak or apex is 

 white. The beak, also, is less prominent. The special ridge, just 

 alluded to, here runs much nearer to the articular ridge, and is less 

 prominent : indeed, in old specimens, it is often almost obliterated. 

 Finally, the whole valve, in proportion to the scutum, is rather broader. 



I have seen a young specimen, about a quarter of an inch in basal 

 diameter, with the orifice of the shell toothed owing to the obliquity 

 of the summits of the radii ; and this gave the shell a very peculiar 

 aspect. The largest w r ell-coloured specimen w r hich I have seen is 1*2 

 of an inch in basal diameter; but in Mr. Cuming's collection there are 

 two rugged, disintegrated specimens, two inches in basal diameter, and 

 two and a half in height. Some specimens, 1*3 in basal diameter, in 

 Mr. Stutchbury's collection, are remarkable from the radii having 

 been obliterated — the shell being merely divided by six sutures, as we 

 have seen is likewise sometimes the case with large specimens of 

 B. iisittacus. 



This species is evidently a South African representative of the South 

 American B. psittacus. 



5. Balanus Nigrescens. PI. 2, fig. 5 a, 5 b. 



Balanus nigrescess. Lamarck, (1818) in Chenu. Must. Conch., 



Tab. 4, fig. 16. 



— gigas. Ranzani. Memoire di Storia Nat., 1S20, Tab. 3, 



fig- 5, 0, 7. 



— — J)e Blainville. Diet, des Sc. Nat., Tab. 11G, 



fig. 2, 2 a. 



Shell cinereous, tinted with pale or blackish blue, orivhollg 

 white. Scutum tvith the articular ridge terminating down- 

 wards in a small, sharp, free point : adductor ridge prominent. 

 Tergum with the apex produced and needle-like. 



Hub. — Swan River, West Australia, Mus. Brit., attached to sandstone. 

 Attached to sandstone and to each other in a group, Mus. Cuming. Twofold 

 Bay, S. E. Australia, attached to tidal rocks and Patellae, Mus. Darwin. 



