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General Remarks: The specimens from the two stations correspond sufficiently to 

 consider them as belonging to the same species. In minute details of size and colour, and in 

 less important points of the structure of the animal's body, the correspondence, perhaps', is not 

 complete; yet it is certainly great enough to put them together. Should the species, which, 

 though not a true deep-sea species, inhabits deeper water (of about ioo m.), be collected again, 

 so that richer material can be investigated, its relations with other species will have to be 

 settled. With the present material this could not be done in a satisfactory way. 



5. Sectio: Membrano-Balanus 

 15. Balanus longirostrum n. sp. PI. XX, fig. 8 — 16. 



Shell quite imbedded in a sponge ; parietes solid ; basis membranous ; rostrum twice as long 

 as carina, with the basal part narrow, and a longitudinal furrow over its whole length. Carino-lateral 

 compartments very narrow. Scutum with two longitudinal folds. Tergum with the spur broad. 



This species is nearly related to Balaiuts declivis Darwin from the West-Indies. Paying 

 special attention to the little differences I found between this form from the Malay Archipelago 

 and Darwin's description and figures, I thought better to describe the Siboga-species as new, 

 although convinced that, in several respects, it corresponds with the West-Indian form. 



The shell (PI XX, fig. 8) is thin, brittle, smooth and white; the membrane which 

 covers B. declivis is not, or not so well-developed in the present species : only small parts of 

 it are observed round the orifice ; no bristles are seen clothing this membrane. The parietes 

 are not porose, they are delicately striated longitudinally, much more distinctly in horizontal 

 direction. The orifice is large and irregularly toothed. The carina and the rostrum are both 

 strongly bowed ; but, while the carina is only a trifle longer than the lateral compartments, 

 the rostrum (PI. XX, fig. 9) is about twice as long, the basal part extending far beyond the 

 basal margin of the other compartments. This basal part is broader upwards, grows narrow 

 downwards and terminates almost in a point. The exterior surface of the rostrum is longitudinally 

 grooved by a furrow which extends almost to the pointed basis. The alae are broader and 

 horizontally striated in the same way as the compartments ; the radii are narrow, their summits 

 are somewhat oblique, their sutural edges smooth. The carino-lateral segments are about the 

 same length as the lateral compartments, which, however, are three times as broad as the 

 former. One of the larger specimens I have examined has a basal diameter of about 4 mm. 

 and a height of 2 l / t mm. The length of the rostrum of this specimen was over 5 mm. 



The scutum (PI. XX, fig. 10, a and c) is distinctly convex, with very narrow lines 

 of growth, very feebly crenated, so as to produce a hardly visible longitudinal striation. It 

 shows two longitudinal furrows dividing it indistinctly into a broader middle, and two narrower 

 lateral parts. On the inner surface there is no adductor ridge, and the articular ridge is moderately 

 developed, broadest in the middle and sloping towards the inferior extremity. The pit for the 

 depressor muscle can hardly be distinguished. 



The tergum (PI. XX, fig. 10, b and d) is beaked, with the scutal margin straight. 

 The external surface shows distinct growth-ridges. The spur is situated close to the basi-scutal 



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