[52 THE VOYAGE OF H.M.S. CHALLENGER. 



Section D. Parietes permeated by pores. Basis and radii not permeated. 

 Balanus rostratus, n. sp. (PI. XIII. figs. 16-22). 



Shell white, smooth, not covered by membrane. Carina-lateral compartments very 

 narrow; radii narrow, with their oblique summits rounded. Scutum longitudinally 

 striated ; tergum with a broad and blunt spur. 



This species has a very characteristic shape, partly caused by its small orifice, partly 

 by the great development of the rostrum and the narrowness of the carino-lateral com- 

 partments (PI XIII. fig. 16). In this respect it resembles Balanus Icevis, and especially 

 the var. nitidus. However, in this species the basis is permeated by pores, and the scutum 

 has longitudinal furrows, which two characteristics are wanting in the present species. 



The section D of Darwin contains four species. The first, Balanus porcatus, 

 remarkable for the form of its tergum, which has a produced and purple apex; the 

 second, Balanus patellaris, with a depressed shell of a brown-violet colour, and 

 an elongate rhomboidal orifice; the third, Balanus avuatus, the radii of which 

 are rough and straight, and are furnished with oblique summits and with a scutum 

 without an adductor ridge ; the fourth, Balanus glandula, with imperfect and small 

 pores in the parietes, which are sometimes in part absent. With none of these does 

 the present species quite correspond, though no doubt it is nearly related to Balanus 

 glandula, and also to Balanus crenatus. 



The shell is conical, white, smooth ; neither covered by membrane nor furrowed. 

 The orifice is small and irregularly toothed. Radii very narrow, with rounded, oblique 

 summits ; the sutural edges of the radii are crenated. The aim are also narrow, they 

 have rounded, oblique summits like the radii. The pores of the parietes are very wide 

 in the lower half of the valves, they are a great deal narrower in the upper half. The 

 base is thin ; it is finely furrowed in lines radiating from the centre. The sheath extends 

 almost half-way down the valves ; the extreme narrowness of the carino-lateral compart- 

 ments in this species is very remarkable ; in this respect the species comes very near 

 to Balanus quadrivittatus, Darwin. The rostrum, on the contrary, is very highly de- 

 veloped, and forms a broad, flat valve (PL XIII. fig. 17). 



The scutum (figs. 19, 20) shows very prominent lines of growth, and is distinctly 

 striated longitudinally ; the lines of growth are divided into squarish beads by the striae ; 

 the angle formed by the tergal and basal margins is very much truncated. Internally 

 the articular ridge is rather long, but not very prominent ; the adductor ridge is 

 distinctly visible, and extends high up on to the superior part of the valve, running almost 

 parallel to the articular ridge ; the pit for the adductor muscle is hardly visible ; the 

 cavity for the depressor muscle is rather deep. The tergum (figs. 18 and 21) shows traces 



