REPORT OX THE CALCAREA. 65 



are also O'lo mm. long, but there are, moreover, chiefly on the outer surface, spicules 

 reaching 0*2 mm. in length; in both cases the proportion between the length and the 



thickness of the rays being 15 : 1, and the rays of rather cylindrical form. According to 

 his theoretical speculations, Hteckel gave to the species in his Monograph another name. 

 We knmv, however, that the speculations alluded to have no real foundation, and there- 

 fore I propose to return to the older specific name of the Sponge in question. 



Colour. — Dirty y ellowish. 



Habitat. — Station 149, Balfour Bay, Kerguelen Island, January 19, 1874 ; depth, 

 20 to GO fathoms. Station 150, February 2, 1874; hit. 52 Q 4' S., long. 71° 22' E. ; 

 near Heard Island; depth, 150 fathoms; rock. 



Leuconia dura, n. sp. (PI. II. fig. 3 ; PI. VII. figs. 7a-7a f "). 



This species is represented in the collection by many colonial and solitary forms from the 

 Bermudas, and by one colonial specimen from Australia. This latter may be seen drawn 

 in its natural size on PI. II. rig. 3. All the specimens are either bare-mouthed or pro- 

 vided with a collar, and their inner cavity is either still distinguishable, although more 

 or less short and narrow, or reduced (Australian specimen) to a small hollow space jusl 

 under the osculum. The skeleton consists principally of large and small regular 

 triradiate spicules, the latter showing occasionally the rudiment of the fourth ray 

 (Australian specimen). The measurements of these smaller and larger regular triradiate 

 spicules agree closely with those given by Hteckel for his Leucetta primigenia, var. 

 microraphis (specimen from Bermudas), and var. megaraphis (specimen from Australia). 

 There are, however, two distinctions: in Leicconia dura, in company with the regular 

 spicules, are also others, which, although of the same dimensions as the smaller regular 

 triradiate spicules, are yet either sagittally, or sometimes, though not often, irregularly 

 differentiated. These chiefly sagittal spicules are to be found only in the region of the 

 osculum ; they prove, consequently, the permanence of the presence of this latter, and this 

 forms the second difference, the varieties of Leuconia f rut icosa being, according to Hteckel, 

 sometimes furnished with oscula, sometimes mouthless. The spicules in question are repre- 

 sented on PL VII. fig. 7 ; they have, apart from their size, just the same form as the 

 corresponding triradiate spicules of Leucosolenia poterium (?), Leucetta vera, and In ua tta 

 hceekeliana. We learn from this coincidence that the horn-shaped form of spicule 

 is very well adapted for constituting the skeleton of the borders of the osculum or of 

 the membrana oscularis. It is not, however, always the case. The corresponding spicules 

 in Leuconia f rut icom just described show no difference in their form from the other 

 spicules of the sponge, and as the regular triradiate spicules are comparatively very constant 

 in their outlines, I think I am right in concluding that their local differentiation into 



(ZOOL. CHALI. EXP. — PART XXIV. — 188;'.) A;l '.• 



