276 balanid^:. 



different direction, we are reminded of B. calceolus and its 

 allies; and these latter we know can hardly be separated from 

 certain species of Acasta. Hence the position of our pre- 

 sent species in this section, is not natural ; but I am unable 

 to place it elsewhere, without breaking down every de- 

 finition : it should stand somewhat isolated, on one side of 

 a line of affinity connecting Balanus calceolus and navicula 

 with Acasta jourpurata. 



General Appearance. — The shell is thin, fragile, smooth, and white, 

 but covered to a considerable extent by a brown membrane, which on 

 the sheath and opercular valve is of a bright tint, and clothed with 

 bristles. Viewed laterally, the rostrum is seen to be considerably 

 bowed, and from its being nearly twice as long as the other compart- 

 ments, with its lower end bluntly pointed, the basal margin of the whole 

 shell is rendered very oblique, forming a slightly concave line. The 

 lateral compartments are rather longer, and about one third broader 

 than the carino-lateral compartments. The rostrum, from terminating 

 downwards in a blunt point, instead of being square or truncated, as 

 in all other Cirripedes, and from the upper end being, as is usual, 

 pointed, has, when disarticulated from the other compartments, the 

 shape of a boat. The parietes are not at all porose : their internal 

 surface sometimes shows traces of longitudinal ribs, but sometimes 

 there are none. The radii are narrow, with their summits very 

 oblique, and their sutural edges smooth. The sutural edges of thealae 

 are likewise smooth. The largest of Mr. Cuming's specimens was 

 •2 of an inch in diameter ; but a disarticulated specimen in the British 

 Museum must have been larger, having a rostrum *3 in length. The 

 Basis is membranous. 



The Scuta are rather convex ; they have their lines of growth 

 approximate, most finely crenated, so as to be very feebly striated longi- 

 tudinally. Internally, the articular ridge is pretty well developed, its 

 lower edge being very oblique ; there is barely an adductor ridge : the 

 pit for the lateral depressor muscle is deep. The spur of the Tergum 

 is placed close to the basi-scutal angle of the valve ; it is about half as 

 wide as the valve, with the lower end truncated : sometimes it may be 

 rather said to be bluntly pointed, owing to its carinal side sloping up 

 to the basal margin. The articular ridge is pretty well developed. 

 The crests for the depressor muscles are barely discernible. 



AnimaVs body unknown. 



