REPORT ON THE RADIOLARIA. 1679 



The ideal fundamental form of the shell, however, is constantly monaxonian, since the 

 place of the shell-mouth and of the proboscis of the capsule (both lying in one axis of 

 the sphere), causes a principal axis to be different from all others. The longer radial 

 spines, quite variable in number and disposition, are never arranged regularly or 

 symmetrically, and therefore determine no constant axes. 



The lattice-work of the spherical shell offers also but slight differences. It is 

 usually more or less irregular, with circular or subcircular pores of unequal sizes. More 

 rarely the network is perfectly regular, with equidistant circular pores of equal size, 

 and sometimes these are surrounded by hexagonal frames (fig. 6), as in many 

 Sphseroidea. More rarely the pores are perfectly irregular, roundish or sometimes 

 polygonal, of unequal sizes and dissimilar forms (fig. 2). The size of the pores is very 

 variable, between O'Ol and 0'05, usually between G'015 and 0'025. They are commonly 

 somewhat broader than the bars between them, more rarely smaller. The substance of 

 the shell-wall is in the majority of Castanellida hyaline, transparent (as in the similar 

 Sphseroidea); in some larger forms, however, a network of fine axial filaments is 

 visible in the lattice (fig. 2), and sometimes this seems to be hollow, with an axial 

 canal (as in the large Orosphserida). Such an axial filament or fine axial canal is 

 usually visible in the larger radial spines. The shell-wall of the Castanellida, however, 

 never exhibits that characteristic structure (with tangential needles in a cement- 

 like fundamental substance), which we find in all Circoporida. The latter differ also in 

 the constant presence of circles of large pores around the bases of the radial spines, 

 which are never found in the Castanellida. The shell becomes usually stained more or 

 less purple by carmine, and when burned by fire, becomes of a brown colour. 



The inner surface of the shell is always quite smooth, the outer surface armed 

 with numerous short and thin radial bristles. Sometimes these bristles or " by-spines " 

 are very short, but never perfectly wanting. Usually their length is about one-third 

 or one-fourth of the radius of the shell, often less, rarely more. They arise from the 

 nodal points between every three or four neighbouring spines, and are commonly very 

 thin and straight, pointed, with slightly thickened conical basis. Rarely they are 

 directed not quite radially, but more or less obliquely. 



The larger radial spines, which arise between the thin bristles or " by-spines " and 

 may be opposed to the latter as " main-spines," are wanting in two genera only, in 

 Castanarium and Castanella (PL 113, fig. 6). They are simple in Castanidium 

 (figs. 2, 5, 7) and Castanissa (fig. 1), irregularly branched in Castanopsis and 

 Castanura (figs. 3, 4). Their number and disposition is never regular nor symmetrical 

 (as in the majority of Sphseroidea) and varies even in each single species. In 

 general the number of main-spines varies between ten and forty (rarely less or more) 

 usually between twenty and thirty. Their length is commonly about equal to the 

 diameter of the shell, often somewhat shorter, rarely considerably longer. Their 



