(sect, c), balanus perforatus. 233 



much elongated, owing to the basis becoming deeply cup-formed : I 

 have seen specimens, half an inch in diameter in the widest part, one 

 inch and a half in height, the walls forming only a third of this. The 

 largest specimen which I have seen (from the southern shores of 

 England) had a basal diameter of 1*2 of an inch ; some very steeply 

 conical specimens were "9 of an inch in height, and "8 in basal 

 diameter. 



Scuta, externally, slightly convex ; growth-ridges approximate, mo- 

 derately prominent. Internally (PI. 4, fig. 3 a) the articular ridge is 

 moderately developed, with the lower end produced downwards into a 

 freely depending, flattened style, somewhat variable in size, but not so 

 long as in B. laevis, and easily broken in disarticulating the valves. 

 The adductor ridge is very prominent, running from almost the apex 

 of the valve, close to the articular ridge, to near the basal margin. 

 The basi-tergal portion of the valve is converted by the adductor ridge 

 into a rather deep cavity, within which there is a short, sharp, and 

 minute ridge, close and parallel to the adductor ridge, and bounding the 

 impression left by the lateral depressor muscle : this insignificant ridge 

 was present in every specimen ; it occurs only in very few other species, 

 as in B. nubibus and cariosus. The thickness of the valve sometimes 

 varies a little, and wheu thick the adductor ridge does not appear quite 

 so prominent. Tergum, with the apex moderately beaked and pro- 

 duced ; beak triangular in section, coloured dark purple, as is the upper 

 internal surface of the valve ; the longitudinal furrow is deep, and has 

 its edges folded in, and even quite closed. The spur is moderately long 

 and narrow ; but its width varies a little (PI. 4, fig. 3 b, 3 c), and con- 

 sequently it stands at either rather above or at twice its own breadth 

 from the basi-scutal angle : its lower end is either bluntly pointed or 

 square, and generally is feebly toothed on the under-side. The basal 

 margin of the valve generally slopes a little, on both sides, towards the 

 spur. Internally, the scutal margin is but slightly inflected : the 

 articular ridge is but slightly prominent, and but little curved ; in the 

 upper part of the valve there are generally several very minute ridges, 

 parallel to the articular ridge, on the side towards the scutum. The 

 internal surface of the spur itself is sometimes concave. The crests 

 for the carinal depressor muscle are barely developed. It may here be 

 mentioned that on the opercular membrane many long spines stand 

 rudely arranged in rows. 



Parietes : the parietal tubes have not transverse septa ; but are 

 solidly filled up in their upper parts by dark-purple layers of shell. 

 The radii, as already stated, are either not at all developed, or are 

 extremely or only moderately narrow, with their summits more or less 

 oblique : in Mr. Cuming's collection, however, there is an unique 

 specimen, var. mirabilis (PI. 5, fig. 1 c) with the aperture of the shell 

 as wide as the basis, with bright purple parietes, and white, very broad 

 radii, having their summits parallel to the basis. The septa of the 

 radii are finely denticulated, and the interspaces are filled up solidly. 

 The alee have very oblique summits, and their edges are finely crenated. 

 Basis, flat, or deeply cup-shaped; there is often an underlying, 

 coarselv-cancellated layer. 



