138. _Radial Spines of the Nassellaria._--The radial spines in this legion show as great a variety in their form as in the SPUMELLARIA, and, as in them, are solid, siliceous bars, usually three-edged (prismatic or pyramidal), or round (cylindrical or conical); more seldom they are polygonal in section. The great majority of the NASSELLARIA are, however, distinguished by a triradial structure, three primary radial bars diverging from the base of the central capsule (usually from the centre of the porochora); there is usually in addition a fourth apical spine, which passes upwards vertically or obliquely on the dorsal aspect of the central capsule. These three or four typical radial spines of the NASSELLARIA may be derived with great probability from the basal tripod of the #Plectoidea# (_Plagoniscus_, _Plectaniscus_, &c., Pl. 91); and since this tripod is very characteristically combined in _Cortina_ and _Cortiniscus_ with the primary sagittal ring of the #Stephoidea#, the three typical rays may be generally designated "cortinar feet," in contradistinction to the other radial processes of the NASSELLARIAN skeleton. One of the three descending basal feet ("pes caudalis," Pls. 91-95, C) is always unpaired, and lies in the vertical median plane (or sagittal plane), just as does the vertically directed apical spine, which originally forms the dorsal bar of the sagittal ring, and is produced upwards into the "apical horn," (marked _a_ on the plates). The other two basal feet are paired, and diverge right and left, forwards and downwards ("pedes pectorales," _p.p._). Six-rayed NASSELLARIA, in which three secondary (interradial) feet are intercalated between the three primary (perradial) cortinar feet, are less common than the three-rayed forms. In some groups the number rises still higher, nine, twelve, or even more secondary feet being intercalated between the three primary. Besides, accessory radial spines may be developed on different parts of the shell, which have sometimes a definite relationship to the typical radial spines, sometimes not. Their form and ramification are very various (Pls. 51-98).