222 balanidyE. 



This is a very distinct form, though nearer to the 

 foregoing than to the other species. Its separation from 

 the sub-genus Acasta is quite artificial ; its affinity to this 

 sub-genus is shown by its weaker shell, non-porose parietes 

 and basis ; by the radii having their sutural edges smooth, 

 and their summits not quite square ; by the carino-lateral 

 compartments being very narrow ; by the less elongated 

 basis, not furrowed, from not clasping the branches of the 

 Gorgon ia ; and by the longitudinally striated scuta ; never- 

 theless, from the similar habits, and from the graduated 

 structure in the five foregoing species, it cannot be removed 

 out of the genus Balanus. I have seen three sets of speci- 

 mens of this species. 



General Appearance. — Shell, sometimes with the rostrum, and some- 

 times with the carina, and corresponding portions of the basal cup, 

 elongated ; but not, apparently, to so great a degree as in the foregoing- 

 species ; basis not furrowed, from not clasping the branches of the 

 Gorgon ia. Colour pale bltieish-purple, with the radii whiter. The 

 surface is studded with small calcareous points. The carino-lateral 

 compartments are very narrow, not more than one tenth of the width 

 of the lateral compartments ; they are, moreover, scarcely wider at the 

 base than at the summit. The summits of the radii are, apparently, a 

 little oblique, or at least not so square as in the foregoing species.. 

 The shell is not nearly so strong as in the last three species; and the 

 compartments separate by gentle force, and from the action of caustic 

 potash. The largest specimen was *4 of an inch in basal diameter. 



Internally, the parietes are not very strongly ribbed, or they are 

 almost smooth, and there are no pores. The basis is concave and 

 smooth within, and is not porose. The sutural edges of the radii are 

 quite smooth, or sometimes they exhibit, in the lower part, mere traces 

 of septa, — a character by itself sufficient to separate this from the 

 foregoing species. The alse have oblique summits, and the rather narrow 

 portion added during the diametric growth of the shell, is white. 



The Scutum, externally (6 d), has raised striae, radiating from the 

 apex ; valve rather thick ; internally, the articular ridge is but slightly 

 prominent, and its lower end is rounded off: the depression for the 

 lateral depressor muscle is slight ; between this depression and that 

 for the adductor muscle, the surface of the valve is prominent. 

 Tergum, somewhat beaked ; externally, the surface is depressed in the 

 line of the spur: the carino-basal margin slopes towards the spur. 



Animals body unknown. 



