474 BALANIDiE. 



ture is there plainly seen. In extremely young shells the holes are not 

 present ; but very soon, at four points of the circumference, namely, 

 two in the carina and one in each lateral compartment, the basal edge 

 becomes indented, and during growth more and more deeply indented ; 

 at last the horns or points of the bays, thus formed in the circumference 

 of the shell, grow inwards and meet, the four indentations being thus con- 

 verted into four rings or holes ; as the shell is added to, at its circumfer- 

 ence, these come to stand further and further from the exterior margin ; 

 and as the shell at the same time rises above the surface of attachment, 

 the holes are added to at their basal edges, and are thus converted into 

 shelly tubes, generally freely open at the bottom as well as at the top. 

 Sometimes these tubes are closed at the bottom, and this is usually 

 caused by their sides having been added to in a spiral direction. A some- 

 what sinuous double ridge or fissure, leading from the tubes or holes to the 

 exterior border, can always be perceived on the under side of the shell. 

 Occasionally, though rarely, in very old shells, a second series of holes 

 is formed outside the first four holes, and often a tendency to this 

 may be perceived in the just-mentioned fissures expanding a 

 little at their outer ends, thus forming four new circumferential 

 indentations. The purpose of this peculiar structure, apparently, is to 

 give support to the much depressed and thin shell. In Chthamalus 

 stellatus and scab?'osus, we have seen a slight indication of a similar 

 structure, in the formation on the under side of the shell, but con- 

 fined to the lines of sutures, of obscurely tubular pillars : we have 

 also something analogous in the singular midribs, in Platylepas, 

 causing the membranous basis to be convex. I need onlv further 

 add, that the parietes, in Chamsesipho, are rather thin, and are com- 

 posed of translucent shell, punctured for the entrance of tubuli, with 

 the punctures often arranged in straight lines. 



Opercular Valves (fig. 4 d). — These are attached by a narrow opercu- 

 lar membrane to the sheath, but little beneath the summit of the shell. 

 The Scuta are considerably arched or convex : the articular ridge is 

 very prominent, and there is a thick strong adductor ridge. The Terga 

 have a short, rather broad, rounded spur, placed very nearly in the 

 middle of the valve : the crests for the tergal depressores are moderately 

 developed, and are simple. 



Mouth. — The crest of the labrum is hairy, and is much hollowed 

 out. The palpi are small and narrow, with long bristles at their 

 apices. The mandibles have four or five teeth, with the lower part 

 pectinated. The maxillae are notched. Of the Cirri, the second pair 

 is short, and all the segments are thickly clothed with bristles. The 

 third pair in the arrangement of the bristles resembles the four pos- 

 terior pairs. The segments in these pairs are elongated, and support 

 four pairs of main spines. 



I was not able to observe any Branchiae. 



