132 Mr. H. J. Carter on 



the arms of the triradiates. Vent single and terminal In the 

 individualized solitary forms, in plurality in the flat ones, in 

 which they are more or less uniformly scattered over the sur- 

 face in a papillated state, about ^ inch apart, each furnished 

 with a minute peristome, which consists of mortar-spicules 

 like those that fringe the pores of the dermal cribriform sar- 

 code ; leading in the globular forms into a regularly formed 

 cloaca corresponding in shape with the specimen, and into 

 irregularly branched canals in the flat ones ; holes of the 

 cloaca of different sizes and different distances apart, the 

 largest more or less sunk into the internal structure, and all 

 affording outlets to a variable number of excretory canals ; 

 surface of the cloaca, together with that of the holes and their 

 subsequent extensions respectively into the internal structures, 

 thickly echinated with small s])ines, viz. the fourth arms of 

 the quadriradiates. Wall composed of cancellated structure, 

 that is the parenchyma, traversed by the canals of the excre- 

 tory system, supported on a skeletal structure composed of 

 sm.all triradiates. Spicules of three kinds, viz. acerate, tri- 

 radiate, and quadriradiate : — 1, acerates, minute, sinuous, 

 and lanceolate at one end, about 14 by ^-GOOOth in. ; 2, tri- 

 radiates, of two sizes, viz. those of the wall-structure, which are 

 small and more or less regular, and those of the surface, 

 which are large, averaging 105 by 9-6000ths in. in the shaft, 

 with arms respectively a little less ; 3, quadriradiates, with 

 long expanded arms and very short spine or fourth ray. No. 

 1 is confined to the cribriform sarcode of the surface and to 

 the peristome, where in the former it acts as a raortar-spicule ; 

 no. 2 chiefly to the structure of the wall and the surface 

 respectively, as before stated ; and no. 3 to the surface of the 

 cloaca, where the spines or fourth rays are so small and short 

 that they can only be seen laterally. Size of globular form 

 about 4-12ths inch high and 3-12ths inch in diameter hori- 

 zontally ; the flat form is merely a fragment about an inch in 

 diameter and l-24th inch thick. 



Obs. With the exception of trifling differences, the Aus- 

 tralian species in its flat form is almost identical with the 

 British one called Leuconia nivea^ Bk. {Leucandra nivea, H., 

 Atlas, Taf. xxxix.) — that is, there are no quadriradiates like 

 those represented by Bowerbank (Mon. vol. iii. pi. v. fig. 8), 

 and the elements of the surface in L. nivea appear to be much 

 more confused and indistinct, while they are beautifully 

 defined in the Australian form ; but in other respects the 

 latter appears to be so nearly allied to the British one that it 

 can hardly be considered more than a variety of it. 



