154 THE VOYAGE OF H.M.S. CHALLENGER. 



Torres Strait, the second time near Hiogo Harbour, Japan. The surface of the .shell is 

 beautifully striped with pinkish -purple ; the specimens from Kobe, Japan, are darker, 

 almost rose-coloured, and have the shell conical; those of Torres Strait are slightly more 

 cylindrical, and have the orifice larger. 



Hitherto the species was only known from the mouth of the Indus, from the East 

 Indian Archipelago, from the Philippine Archipelago, from Moreton Bay (Australia), and 

 from the north-east coast of Australia. So our knowledge of its distribution is slightly 

 augmented by its being observed also in Japan. 



Station 18G, September 8, 1874; hit. 10° 30' S., long. 142° 18' E. ; depth, 8 fathoms ; 

 bottom, coral sand. Station 233a, May 17 to 10, 1875 ; hit. 34° 35' N., long. 135° 10' 

 E. ; depth. 8 and 50 fathoms; bottom, mud and sand. Kobe, Japan. 



Bala n us tenuis, n. sp. (PL XIII. figs. 29-33). 



Shell snow-white, glossy ; orifice deeply toothed. Eadii narrow, with their summits 

 very oblique and slightly concave; basis solid. Scutum striated longitudinally; 

 tergum with a short and rather broad spur. 



This species, in many respects, corresponds to Balanus amaryllis, Darwin, and 

 especially to the variety (b) of Darwin. Yet I think it is different; if we knew 

 something about the origin of this species, we should perhaps consider it as the form 

 which had developed from the other under the changed conditions of the deep sea. 

 Darwin tells us that Balanus amaryllis was often met with attached to ships' bottoms, 

 and as the present species was taken from 100 fathoms, we may safely call it a deep- 

 sea species in comparison with the other. 



In the collection made during the cruise of H.M.S. Challenger this species is 

 represented by four small specimens only. The greatest diameter of the base of the 

 largest specimen is 7 '5 mm. The height of this s]jecimen is not more than 5 mm. The 

 compartments are extremely steep ; hence the toothed orifice is large. This orifice has 

 the shape of a pentagon. The different compartments are striated longitudinally, caused 

 by the internal longitudinal ribs being visible through the transparent surface, and, 

 though not so distinctly, also transversely. However, the surface is smooth and even 

 glossy. The radii are well-developed, though narrow ; their upper edges are extremely 

 oblique. The internal surface of the compartments is very strongly ribbed. The basis 

 is very thin and shows ribs also, which, however, are solid. 



Scvta (figs. 30 and 32) triangular, not elongated, distinctly striated longitudinally. 

 Internally the articular ridge reaches beyond half the tergal margin ; it is rather pro- 

 minent, The adductor ridge is only slightly developed ; the cavity for the depressor 

 muscle is narrow. 



