REPORT ON THE RADIOLARIA. 1537 



The skeleton of the PHJEODARIA is always extracapsular, and exhibits in the majority 

 of this legion such a characteristic shape, form, and structure, that these organisms 

 may be easily recognised by it, even apart from the central capsule and the phseodium. 

 In a few cases, however, the skeleton is so similar to that of some NASSELLARIA and 

 SPUMELLARIA, that it may be accidentally confounded with it. In general the skeleton 

 of the PH^EODARIA is much larger, and much more highly developed, than that of most 

 other Radiolaria, and exhibits the most wonderful appearances, and the most 

 marvellous complications, which are found in the whole world of Protists, or of unicellular 

 organisms. The varied composition and differentiation of the skeleton alone distinguishes 

 the numerous families, genera, and species of PH^EODARIA described in the sequel ; 

 all the fifteen families, however, agree so completely in the structure of the central 

 capsule and the phseodium described, that we may derive them all phylogenetically 

 from a small skeletonless family, the Phseodinida. 



The chemical composition of the skeleton seems to be, in the majority of PH^EODARIA, 

 somewhat different from that of the other Radiolaria. In a few groups only, especially 

 in the Cannobelida ( Piety ocha, Mesocena, &c.), and in a part of the Castanellida and 7 

 Concharida, the substance of the skeleton seems to be of pure silica, as in the NASSELLARIA vjuMy^ ^ 



and SPUMELLARIA ; these flinty skeletons, therefore, may be also found fossil. In the 1 



majority of PH^EODARIA, however, the skeleton does not consist of pure silica, but of 

 an organic silicate ; it becomes more or less intensely stained by carmine, and 

 browned or blacked by fire ; in many cases it even becomes completely burned and 

 destroyed by the prolonged action of heat. This circumstance explains why PH^EODARIA 

 in general are rare in deep-sea deposits, as in the common Radiolarian ooze of the 

 Pacific, and why they are generally absent in fossil deposits. Even the pure Radiolarian 

 rocks of the Barbados, &c., contain only a few PH^EODARIA, mainly Dictyochida. 



According to the different forms of the skeleton, we may divide the legion or sub- 

 class of PH^EODARIA into two sublegions, four orders, and fifteen families. Firstly, we 

 may distinguish as two groups the Phseocystina, without a lattice-shell, and the 

 Pheeocoscina, with a lattice-shell (compare above, p. 5). The Phseocystina 

 comprise three different families, viz., (l) Pha3odinida, without any skeleton (PI. 101, figs. 

 1, 2); (2) Cannorrhaphida, with an incomplete skeleton, composed of numerous separate, 

 not radial pieces, which are scattered around the capsule in the calymma (PI. 101, figs. 

 3-14; PL 114, figs. 7-13), and (3) Aulacanthida (PI. 102-105), with an incom- 

 plete skeleton, composed of numerous hollow radial tubes, which pierce the calymma 

 and come in contact by their proximal ends with the surface of the central capsule. 



The Phseocoscina, or the PH^EODARIA with a lattice-shell (embracing the great 

 majority of the whole legion) exhibit three principal differences in the shape of their shell, 

 and from these we distinguish the three following orders ; (A) Phseosphseria, 

 with a spherical, not bivalved shell (rarely of an ellipsoidal or lenticular, or another 



(ZOOL. CHALL. EXP. - PAET XL. 1886.) Rr 193 



