314 balanidjE. 



Shell white, with numerous approximate longitudinal 

 ribs : radii broad, with their summits slightly oblique, inter- 

 nally porose : tergum with the articular ridge extraordi- 

 narily prominent, with the spur not joined to the basi-scutal 

 angle. 



Hab. — "West Indies, adhering to Balanus eburneus and to Lepas anserifera. 

 New South "Wales, adhering to Tetraclita porosa. Attached to Balanus tintinna- 

 bulum, on a ship's bottom from Sumatra; not rarely attached to Balanus 

 tintinnabulum on ships' bottoms ; Mus. Brit., Stutchbury, and Cuming. 



General Appearance. — Shell white, rather steeply conical, with 

 numerous, approximate, rather narrow, longitudinal, rounded ribs on 

 the walls: in a specimen half an inch in diameter, there were from eight 

 to twelve ribs on each compartment. The outer lamina of shell seems 

 always well preserved. Orifice rounded, trigonal. Radii white, 

 smooth, broad, with their summits only slightly oblique. I have seen 

 one specimen 1*2 in basal diameter, but quarter of an inch is a 

 common size, and very young specimens are unusually frequent in 

 collections. 



Scuta broad, externally not striated longitudinally. The articular 

 ridge is prominent, and the furrow deep, but not in so great a degree 

 as in T. ccerulescens. The adductor ridge is only slightly prominent ; it 

 extends upwards only a little way above the lower end of the articular 

 rid^e, and does not form with the latter a cavitv. There are no crests 

 for the rostral depressor muscle, but there is a little pit, formed by the 

 folding over of the occludent margin. 



Terga. — These valves, when articulated with the scuta (fig. 5 b), pro- 

 ject above them to an extraordinary degree, and are separated from 

 them by a deep, fissure-like hollow, caused by the remarkable promi- 

 nence of the articular ridge of the terga. The upper part of the 

 tergum is not beaked, and does not project freely much above the sack. 

 The valve is large; externally there is a rounded longitudinal furrow. 

 The tergal margin is broadly inflected. The articular furrow is deep, 

 and the articular ridge far more prominent than in any other sessile 

 cirripede, for it projects, as measured from the outside surface, more 

 than half the width of the valve ; and consequently the valve, when 

 viewed vertically from above, almost appears as if formed by the union 

 of three plates, viz., the articular ridge, and the outside surface on 

 each side of the spur. The spur is of moderate width, with the 

 corners rounded : it is placed near, but not close to the basi-scutal 

 angle, so that there is on this side a small portion of basal margin, 



permanent. In this case, T. radiata might be allowed to stand as my own 

 name, considering that Mr. Sowerby's figure is imperfect and is not accom- 

 panied by any description. At first I thought that the present species might 

 be the Lepas mitra of Spengler, (' Skrivter af Naturhist. Selskabet,' 1790, 

 Tab. 6, fig. 5), but the parietes are not described as porose ; and the folds on 

 the walls are too broad ; on the other hand, his description of the opercular 

 valves makes me think this may be the same species. 



