HEPOET ON THE RADIOLAEIA. CXXV 



195. Phaocystina and Plueocoscina. — Whilst the malacoma of all PmEODARiA 

 possesses the characteristics of the legion, and hence justifies the assumption of a 

 monophyletic origin, the skeleton, on the other hand, shows in the different groups 

 such manifold and fundamental variations that a polyphyletic origin of the latter is 

 indubitable. Difierent Phseodinida have commenced the formation of the skeleton inde- 

 pendently, and it has progressed in different directions. In the Phseocystina it 

 remained incomplete and led to the formation of various Beloid skeletons, whilst the 

 PhiBOCoscina developed complete lattice-shells. Both of these divisions too 

 are to be regarded as polyphyletic, since the skeletal forms of the different groups 

 cannot be derived without violence from a common primitive form. 



196. Phceocystina with a Bdoid Skeleton. — The order Phseocystina includes 

 all Ph^odaeia which have no complete lattice-shell ; it contains, firstly, the skeletonless 

 Phajodiuida (the common stem-group of the legion), and secondly, the Phseacanthida, or 

 PhtEODARIA with a Beloid skeleton (§ 115). The latter are divisible into several very 

 different groups (at least two or three) which are probably different in origin. The 

 Aulacanthida (Pis. 102-105) form radial tubes which perforate the calymma, their 

 proximal end resting upon the surface of the central capsule, whilst the distal extremity 

 projects freely outwards. The skeleton of the Cannorrhaphida, on the other hand, is 

 composed of many sejaarate portions which are never radially arranged but are either 

 placed tangentially to the surface of the calymma or scattered irregularly in its gelatinous 

 mass. Furthermore, in the three subfamilies of which this family is composed, the 

 individual skeletal portions are so different that they have probably arisen inde- 

 pendently of each other ; in the Cannobelida they form cylindrical tangential tubes 

 (PL 101, figs. 3—5), in the Catinulida flat basin or cap-like structures (PI. 117, fig. 8), 

 in the Dictyochida hollow rings, from which small pyramids are developed by unilateral 

 formation of lattice-work (PL 101, figs. 9-14 ; PL 114, figs. 7-12). 



197. PhcBOS'phcBria loith a Sphoeroid Skeleton. — The order Phse o sphser i a 

 includes those Ph^odaria which possess a spherical (sometimes slightly modified) 

 lattice-sheU without the characteristic aperture of the Phseogromia. They have 

 probably arisen independently of these, though they may have been derived from 

 the Castanellida by loss of the shell-aperture, which was present originally. The 

 four families which we have distinguished among the P h fe o s p h se r i a, are so 

 different in the structure of their lattice-shell that their phylogeuetic connection 

 is doubtful. In the Orosphserida (Pis. 106, 107) and the Sagospha3rida (PL 108) 

 the whole lattice-sheU consists of a single piece and is unjoiuted (without astral septa) ; 

 in the former it is very firm and massive, with thick laminated trabeculfe and polygonal 

 meshes ; in the latter it is very delicate and brittle, with filiform trabeculse and large 



