139. _Radial Spines of the Phæodaria._--The radial spines of the PHÆODARIA are very clearly distinguished from those of other Radiolaria by the fact that they are usually hollow tubes, rarely solid bars. As a rule, the tubes are cylindrical, often slightly fusiform or conical, their siliceous wall is very thin, and their lumen filled with jelly; a fine thread of silica usually runs in the axis, and in several families is connected by fine transverse threads with the wall of the tube (Pl. 110, figs. 4, 6; Pl. 115, figs. 6, 7). The peculiar family Medusettida is characterised by a very remarkable segmentation of the hollow spines (Pls. 118-120). Each tube is divided by a series of septa into chambers, which communicate by a central or excentric opening in each septum, an arrangement resembling the siphuncle of the chambered Cephalopod shells. The number and {xcii}arrangement of the radial tubes in most PHÆODARIA is indefinite and very variable; only in a few families is the number constant in each species and genus, and the disposition regular. The Medusettida (Pls. 118-120) resemble the NASSELLARIA, inasmuch as equal radial feet diverge from the base of their shell, sometimes three in number (_Cortinetta_, Pl. 117, fig. 9), sometimes four (_Medusetta_, Pl. 120, figs. 1-4), sometimes six (_Gazelletta_); _Gorgonetta_ is specially distinguished by the possession of six ascending and six descending spines regularly alternating (Pl. 119). The Tuscarorida (Pl. 100) usually have three or four equidistant feet. The Circoporida (Pls. 115-117), on the other hand, rather approach the #Sphæroidea#, their spherical or regular polyhedral shell having a definite number of tubular radial spines, which arise at regular intervals from their angles; _Circoporus_ has six, _Circospathis_ nine, _Circogonia_ twelve, and _Circorrhegma_ twenty radial tubes. Very rarely the tubes of the PHÆODARIA are angular, usually they are round, more or less cylindrical, though they are often bifurcated or even ramified, and exhibit a great wealth of the most delicate appendages; siliceous hairs, bristles, spines, barbed or anchor-like hooks, spathillæ, brushes, circlets, &c. (compare Pls. 99-128).