(sect, b), balanus stultus. 217 



closely allied to B. Ajaw, especially in its operculum, than to 

 the following species; yet the fact of the radii not being per- 

 meated by pores does not permit of its admission into the 

 last section ; and both in habits and structure it undoubtedly 

 comes very near to the following species. Those varieties 

 which are not much elongated, and which have the basis 

 nearly flat, would certainly, if considered by themselves 

 alone, not have gained admission into our present section. 



General Appearance. — Shell conical, somewhat globular, more or 

 less elongated in the rostro-carinal axis, owing to the basal production 

 of the rostrum. Orifice, rather small, entire, oval, pointed at the 

 carinal end. Radii moderately broad, with their summits parallel to 

 the basis. Colour dirty white, often faintly tinged with purple ; 

 sheath, pale purplish-blue. Surface extremely smooth ; the parietes 

 are generally covered (as viewed through a lens) by a very thin, yel- 

 lowish epidermis, giving to the whole a glistening, granular aspect : 

 the radii are generally destitute of this epidermis, and are therefore of a 

 dead white. The basis is concave, and sometimes deeply cup-formed ; 

 it is, how'ever, not symmetrical ; sometimes it is flat. Basal diameter 

 of largest specimen, including the basis itself, 1*5 of an inch in the 

 longitudinal axis ; transverse diameter, 1 inch ; the inequality in the 

 length of the two diameters is rarely so great as in this unusually large 

 specimen. 



Scuta, externally very convex, with the growth-ridges extremely 

 prominent ; basal margin sinuous, the middle portion being prominent; 

 this is best seen in young specimens (PL 3, fig. 2d). Internally, the 

 articular ridge is broad and reflexed. The adductor ridge in the upper 

 part is almost confluent with the articular ridge ; it runs down to the most 

 prominent point of the basal margin ; in young specimens it is sharp and 

 prominent ; in old specimens it is very blunt and little prominent. There 

 is a rather deep hollow for the lateral depressor muscle. In young 

 specimens there is a small, depending, blunt tooth at the basi- tergal 

 angle, which helps to make the basal margin more deeply sinuous. 



Terga, with the longitudinal furrow closed, except on the spur itself, 

 where it is open. The spur is moderately long and broad, but varies 

 in breadth ; it is placed at rather less than its own width from the 

 basi-scutal angle ; its lower end is obliquely rounded ; the basal margin 

 on the opposite sides of the spur, together form a nearly straight line. 

 The whole valve is rather broad. The crests for the tergal depressores 

 are barely developed. 



The Compartments have rather large parietal tubes ; the septa are 

 coarsely denticulated at their bases ; the internal lamina is smooth, ex- 

 cept close to the basis. The radii have their summits parallel tothe basis ; 

 their sutural edges are formed of rather thick septa, which stand at an 

 unusual distance apart from each other, and have perfectly symmetrical, 

 minute denticuli on each side. The interspaces between the septa are 

 filled up solidly to within a short distance of the surface ; but yet not so 



