REPORT ON THE RADIOLARIA. 



opposite transverse processes, the former four crossed ones. By ramification and union 

 of these apophyses arise the lattice-shells of the Acanthophracta (excepting the 

 Sphserocapsida). 



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 P 1 e c- 

 toidea (Plagoniscus, Plectaniscus, &c., PL 91); and since this tripod is very charac- 

 teristically 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," Pis. 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 

 (Pis. 51-98). 



139. Radial Spines of the Phceodaria. The radial spines of the PH^EODARIA 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 fusi- 

 form 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 (PI. 110, figs. 4, 6 ; PL 115, figs. 6, 7). 

 The peculiar family Medusettida is characterised by a very remarkable segmentation of the 

 hollow spines (Pis. 1 18-120). 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 arrange- 



