144 Mr. H. J. Carter on 



surface of the cloaca, but also extending into the canals of the 

 internal structure. Size of specimen f in. in height by 1 In. 

 in diameter. 



Obs. The compactness and consequent whiteness of the 

 structure in this species contrasts strongly with that of Leuco- 

 m'a multifida, if tlie presence of the quadriradiates did not 

 absolutely make the distinction. 



39. Leuconia compacta. 



Specimen massive, sessile, lobate, lobes round, furnished 

 with a plurality of small naked vents, growing on and enve- 

 loping the small stems of a Fucus. Colour whitish, opaque. 

 Surface even, consisting of cribriform sarcode cementing to- 

 gether into compact structure small, more or less regular 

 triradiate and quadriradiate spicules of uniform size and 

 appearance, thickly echinated with \t\j large and much 

 curved acerates. Pores, the holes in the cribriform structure, 

 uniformly small, about 3 to 6-6000ths in. in diameter. Vents 

 in plurality, of different sizes, scattered irregularly over the 

 surface, the largest on the most prominent parts of the lobes 

 respectively ; all without peristome, that is naked, leading 

 into narrow, irregularly defined, cloacal cavities, which branch 

 off into the substance of the body or parenchyma, where they 

 become almost infinitely subdivided ; surface of the cloacal 

 cavities, together with the canals entering them, slightly 

 echinated with the fourth arm of quadriradiates. Structure 

 of the wall, or i-ather body as it may be termed (for these dis- 

 tinctions 1I0W begin to disappear), compact, consisting of 

 parenchyma infinitely divided by the branching and rebranch- 

 ing of the excretory canal-system, as just mentioned ; sup- 

 ported on a skeletal structure consisting of small triradiates 

 and quadriradiates like those of the surface. Spicules of 

 three kinds, viz. acerate, triradiate, and quadriradiate: — 1, 

 acerates, large, stout, unsymmetrically fusiform, much curved, 

 averaging 180 by 21-6000ths ; 2, triradiates, regular and irre- 

 gular, uniformly small, arms averaging 30 by 4^-6000ths ; 

 3, quadriradiates, about the same size, but with the fourth 

 arm, as usual, much shorter than the rest. No. 1 thickly 

 echinates the surface, where the thicker half, which is much 

 curved, is free, and the thinner one is sunk into the substance 

 of the body, with whose spicular structure in size also it forms 

 a great contrast, as may be learned from the measurements 

 above given of the acerates and radiates respectively ; nos. 2 

 and 3 are uniforndy distributed throughout the body, in 

 which the surface of the cloacal dilatations and the large 

 canals respectively are sparsely echinated with the fourth ray 



