iS 5 

 7. Balanus albus n. sp. PI. XVI, fig. 12 — 13, PI. XVII, fig. 1 — 6. 



Shell white, striated longitudinally and, in older specimens, indistinctly folded horizontally. 

 Radii narrow, with very oblique summits; alae broad, with the summits rounded. Scutum with 

 very delicate longitudinal striae; tergum with the spur broad and without a longitudinal furrow. 



This species in many respects resembles B. amaryllis and might be considered as the 

 deep-sea form of that species. 



The shell (PI. XVI, fig. 12) is bulky, about as broad as high, with most of the compart- 

 ments horizontally and longitudinally more or less convex, the orifice large, pentagonal and irregularly 

 toothed, the basis either rounded, or if the object to which the shell is attached is narrow, ovate. 

 The radii are narrow, broader towards the basis, with the summits very oblique, and either 

 straight or feebly hollowed out. The alae are broader, their summits rounded and often 

 partly broken off like the tips of the compartments. The upper parts of the compartments are 

 often damaged, the inferior parts on the other hand are thick and strong, in older specimens 

 especially. The colour is uniformly dirty white; the older specimens are striated longitudinally 

 all over the surface, with a few horizontal growth-ridges. The smaller specimens are more 

 hyaline-white. No epidermis is seen. The compartments have 110 pores, but longitudinal ribs, 

 more strongly developed towards the basis, are seen on the inner side. The sheath is white 

 and horizontally striped. The radii also have no pores; the basis is represented by an 

 extremely thin calcareous plate, which shows numerous ridges extending from the centre towards 

 the periphery; here and there they have the appearance of canals, but I failed to make out 

 canals or pores in a transverse section of this basis. 



Scutum (PI. XVI, fig. 13, a and c) with distinct growth-ridges, and a pearly lustre 

 over the surface, very clelicately striated longitudinally. On the inner surface the adductor 

 ridge is only feebly developed, and the adductor musclé cavity is indicated by two longitudinal 

 grooves; the articular ridge is very prominent, and reaches as far as half die length of the 

 tergal margin. The pit for the depressor muscle is rather deep. 



Tergum (PI. XVI, fig. 13, b and d) with the scutal margin only very feebly hollowed 

 out, accordingly the apex can hardly be said to be beaked. No longitudinal furrow, but a 

 distinct crest runs in a curved line almost from the apex to the extremity of the spur. Spur 

 short, obliquely truncated at the posterior side. That part of the basal margin which lies between 

 the basi-scutal angle and the spur is hollowed out, and not shorter than the anterior margin 

 of the spur. Crests for the depressor muscle only feebly developed. 



The investigation of the structure of the animals body gave the following results : 



Mouth. Labrum (PI. XVII, fig. 1) with the notch wide at the entrance, but not deep; 

 3 small, blunt teeth are situated close together on each side of notch. Edge of lateral parts slightly 

 hollowed out, margin furnished with extremely small hairs, and a few more small indistinct teeth 

 towards lateral extremity. The sub-triangular shield-like portion much broader than it is high. 

 (In one of the specimens quite a row of small teeth is observable along the edge of the labrum). 



Pal pi stout, upper margin nearly straight, basal margin slightly arched, the two 

 separated from each other by a nearly longitudinal distal margin. Hairs of the outer surface scattered 



57 



SIBOGA-EXPEDITIE XXXI b. 24 



