(sect, f), balanus terebratus. 285 



three pairs of spines, of which the lowest pair is minute : in B. allium, 

 and I believe in B. cepa, there are five pairs of spines on each 

 segment. 



This species differs from the last only in the peculiar 

 colouring, smoother walls, more oblique radii, solid basis, 

 and more especially in the scuta having the lines of growth 

 not crenated, and internally, in the pit for the lateral 

 depressor muscle being so very minute and placed on the 

 basi-tergal edge of the valve. The posterior cirri, also, I 

 believe, differ in the number of the spines which the 

 segments support; nevertheless, I cannot feel confident 

 about the specific distinctness of B. quadrivittatus. 



37. Balanus terebratus. PI. 8, fig. 2 a — 2 b. 



Shell white, stronglf ribbed longitudinally, with the basal 

 margin produced into long points : basis concave, not per- 

 meated by pores, but strongly ribbed externally in radiating 

 lines; the interspaces between the ribs being riddled by 

 minute rounded apertures, often placed in double rows. 



Hub. — Unknown, Brit. Mus., attached to a lamelliferous coral. 



I have in this instance broken through my rule of not 

 describing a Cirripede without examining the opercular 

 valves ; but the species here named is so peculiar, that it 

 would have been a fault to have passed it over. There is 

 but a single specimen in the British Museum, without, as 

 just stated, the operculum, and of course without the 

 animal's body. 



Shell, white, depressed, conical, somewhat elongated in its rostro- 

 carinal axis ; orifice rather small, pentagonal, toothed, elongated. 

 Parietes rather thin, with extremely prominent longitudinal ribs, pro- 

 duced at the basal edge into long spikes : the internal surface is also 

 ribbed, but less strongly than the outside. Radii rather narrow, with 

 oblique, not smooth summits : sutural edges very finely and obscurely 

 crenated. Alee with their summits extremely oblique. Lower edge of 

 sheath closely attached to the walls. The carino-lateral compartments 

 are rather narrow. 



Basis, slightly concave or saucer-shaped ; the circumference is pro- 



