46 Mr. H. J. Carter on 



which is rather compressed, | in. long by ^ in. in its greatest 

 transverse diameter. 



20. Hypograntia medio articulata. 



Individualized. Pyriform, sack-like, peristomed, turned to 

 one side at the fixed or small end, pear-like. Colour grey. 

 Surface miiforraly even, consisting of cribriform sarcode 

 densely charged with mortar-spicules and small radiates, in 

 short, exactly like that of H. intusarticulata. Pores, that 

 is the holes of the cribriform structure, also about the same 

 size, viz. varying under l-360th in. in diameter. Vent single, 

 circular, surrounded by a peristome ; leading into a narrow 

 cylindrical cavity, corresponding in shape with that of the 

 outward form of the body, that is being widest above, where it 

 is a little less in diameter than the maximum thickness of the 

 wall ; surface of the cloaca presenting large subcircular holes 

 separated from each other by a thick and densely spiculated 

 framework, sparsely echinated with thick curved spines (the 

 fourth arm of the quadriradiate) , more or less covered with a 

 thin layer of sarcode which s])reads itself in a cribriform 

 state all over the surface of the cloaca, where it is best 

 seen under the microscope in a dried condition. Structure of 

 the wall in general like that of H. intusarticulata \ also 

 partly " articulate " and partly " inarticulate," but with the 

 small radiates or articulate skeleton occupying the middle 

 portion, the larger ones with their long shafts the outer half, 

 and the smaller ones of this kind the inner quarter of the 

 wall. Spicules of three kinds, viz. acerate, triradiate, and 

 quadriradiate: — 1, acerates of two forms, viz. the long, thin, 

 cylindrical, glistening one of the peristome, and the other, 

 the mortar-spicule, varying in size under 22 by l-6000th in., 

 more or less straight, without lanciform end ; 2, triradiates, 

 small and large, regular and irregular or sagittal, the large 

 ones with straight shafts averaging 60 by 4-6000ths in. and 

 arms about half this length ; 3, quadriradiates, in which the 

 fourth arm is comparatively stout and long. No. 1, in its 

 longest form, is confined to the peristome, and in its shortest, 

 viz. the mortar-spicule, to the dermal reticulation ; no. 2, the 

 triradiates, in their smallest size^ occupy the " articulated," 

 and the larger ones the " inarticulate" portions of the chambers, 

 where their heads are fixed in the cortex and cloaca, and 

 their long shafts traverse the outer and inner parts of the 

 wall respectively, perpendicular to its sides ; no. 3, the 

 quadriradiates, chiefly in the surface of the cloaca, where the 

 fourth arm projects into the interior and is more or less covered 

 with the sarcode which, in a cribriform condition, lines the 



