(sect, c), BALANUS L.EVIS. 229 



Finally, I may add that B. Icevis seems to represent in the 

 southern hemisphere and on the west coast of North 

 America, the B. p erf or aim of Europe and Western Africa. 



General Appearance. — Shell conical, sometimes slightly globular ; 

 surface smooth (that is, not folded), either naked, and in that case 

 white or pale purple, or covered by dirty yellowish-brown membrane. 

 Orifice small, more or less toothed, rarely exceeding one third of the 

 basal diameter. Radii very narrow, often not developed, the six sutures 

 forming in all cases deep and narrow clefts. The largest recent, but 

 much depressed, specimen which I have seen (from the Strait of 

 Magellan) was three fourths of an inch in basal diameter ; specimens 

 growing congregated are often much elongated. I have seen one with 

 the basal cup between two and three times as deep as the height of the 

 compartments. Of the ancient tertiary specimens, the largest had a 

 diameter of three fourths of an inch, and a total length of actually two 

 inches (fig. 2 a) ; another of these fossils had a basal cup in depth 

 equalling four fifths of the entire length of the shell and basis. 



The scutum has either one very broad and deep longitudinal furrow 

 (2 b), or two moderately broad and deep (2 e), or two narrow and 

 deep, or less frequently one narrow and inconspicuous longitudinal 

 furrow (2f); rarely there is not one furrow; sometimes there are 

 none towards the apex, whilst furrows have been formed in the lower 

 part of the valve. In young specimens the furrows extend down to 

 the actual basal margin, but in old specimens they often fall short of 

 this, and, as a consequence, the furrows become crossed by one, two, 

 or three calcareous ridges, which ridges at successive periods formed 

 the basal margin of the valve. The external surface is covered by 

 yellow membrane; and fragments of several successive opercular mem- 

 branes are often attached to the zones of growth. 



Internally the articular ridge is not very prominent, but is remark- 

 able (2 c, 2 d) from its lower point being produced into a long, sharp, 

 sub-cylindrical, free style (like the hinge of a common gate), which is 

 generally broken off in disarticulating the valve from the tergum. The 

 adductor ridge is either sharp and prominent or blunt : it extends up 

 the middle of the valve nearly to the apex, and downwards it trends a 

 little towards the occludent margin. The pit for the lateral depressor 

 muscle is minute but deep : the basal margin is sometimes hollowed 

 out under this pit. Sometimes there is a distinct, but blunt ridge, 

 caused by one of the furrows outside, parallel to the adductor ridge, 

 and placed between it and the little pit for the lateral depressor ; in 

 this case, the basal margin, as viewed internally, is rendered sinuous 

 (2d), as is best exhibited in the great fossil specimens from Coquimbo. 



Tergum (2g). — Spur of moderate length and breadth, with its lower 

 end obliquely truncated and rounded. The longitudinal furrow has its 

 edges somewhat folded in. The basal margin on the carinal side of 

 the spur is sometimes a little hollowed out. The crests for the de- 

 pressor muscles are well developed; but the corner of the valve sup- 

 porting them is extremely thin, and is often imperfectly calcified. 



Compartments. — The parietal tubes are uot crossed by transverse 



