1638 THE VOYAGE OF H.M.S. CHALLENGER. 



whilst the outer is articulated and composed of hollow tangential tubes, like that of the 

 Aulosphserida. This latter family seems to be most nearly allied to the Cannospheerida, 

 and is perhaps derived from them by loss of the inner shell. The possession of a peculiar 

 mouth in this inner shell brings the Canuosphserida nearer to the Phseogromia. The 

 similar Ccelodrymida, in which also two concentric sphserical shells are connected by 

 hollow radial beams, differ essentially in the bivalved shape of the inner shell and the 

 simple, non-articulated, network of the outer shell. 



Only a single species of Cannosphserida has been hitherto known, described and 

 figured in 1879 by E. Hertwig as Ccelacantha anchorata (loc. cit., p. 92, Taf. ix. fig. 2). 

 The rich collection of the Challenger has added to it only four other species, one of 

 which is most nearly allied to the former, whilst the others belong to a separate genus, 

 Cannosphcera (PI. 112). The inner shell is in this latter genus a solid lamella of 

 silica, whilst in the former it is fenestrated. In all other essential points of structure 

 both genera are scarcely different. 



The inner shell is either spherical or ovate and has a diameter of O'l to 0'4 (usually 

 0'2 to 0'3 mm.). A distinct main axis is always marked by the large open mouth on 

 its oral pole. The aboral part of the shell-cavity contains the spherical central capsule, 

 the oral part the dark phaeodium, a part of which is often prominent through the 

 mouth (figs. 1, 2, 4). The wall of the inner shell is a very thin and transparent 

 lamella of silica, which is structureless and solid in Cannosphcera, distinctly fenestrated 

 in Ccelacantha ; the pores of the latter are irregularly rounded and seem to possess a 

 thickened margin. 



From the surface of the inner shell arise numerous thin, tubular, radial beams 

 (twenty to eighty or more) and connect it with the outer shell. These beams are 

 always very thin and straight cylindrical tubules, about twice to four times as long as 

 the diameter of the inner shell, and usually O'OOl mm. broad, or even less. Their 

 basal end at their origin from the inner shell is more or less dilated, often funnel-shaped, 

 so that the surface of the latter appears mammillated (figs. 2, 4). The cavity of the 

 inner shell seems to pass over immediately into the tubular cavities of the radial beams. 

 These latter are sometimes simple, at other times articulated or jointed by a number of 

 transverse septa. The radial beams are covered in all the species observed either with 

 scattered spines (fig. 5) or with verticils of anchor-threads, very thin, filiform, lateral 

 branches which bear a spathilla with three or four recurved teeth on the distal end 

 (figs. 2, 4). 



The outer shell is either spherical or an endospherical polyhedron, the prominent 

 nodal points of which fall into a spherical face. Its diameter is usually from 2 to 3 mm., 

 rarely more than 3 or less than 1 mm. Its structure is the same as described for 

 the Aulosphserida, being composed of hollow cylindrical tubes, which form a loose network 

 and are separated at its nodal points by astral septa. The meshes of the network are 



