Whilst in all Plagonida the branches of the spine remain perfectly free, in all Plectanida, again, the meeting ends of the branches become united and grow together, and by this concrescence a loose network arises, like wickerwork, which partly encloses the central capsule and the central parts of the spines, on which it rests. The meshes of this loose wickerwork are large, either quite irregular, of very different size and form, or more or less regular, with a certain form and arrangement of the meshes, effected by the peculiar kind of ramification. Commonly the siliceous threads of the arachnoidal wickerwork are very thin, often extremely delicate, representing "pseudopodia metamorphosed into silex." Sometimes the wickerwork is spongy. Its surface is constantly rough and bristly, with free ends of the spine-branches, never covered with a regular lattice-plate, as in the #Cyrtellaria# (#Spyroidea#, #Botryodea#, and #Cyrtoidea#). The entire form of the central wickerwork is in the minority of Plectanida quite irregular and indefinite; in the majority, however, a certain more or less regular entire form is recognisable, effected by a certain, more or less regular origin and mode of the connection of the meeting branches. So in some species of _Triplecta_ (Pl. 91, fig. 7) the network represents a triangular plate, of _Plectophora_ and _Plectaniscus_ a three-sided pyramid, of _Tetraplecta_ (Pl. 91, fig. 3) a tetrahedron, and in many other species a polyhedron of more or less regular form. Some species of Plectanida become very similar to certain species of #Stephoidea#, #Spyroidea#, and #Cyrtoidea#; so _Plectaniscus_ and _Periplecta_ approach to _Cortina_ and _Cortiniscus_, _Pteroscenium_ and _Clathrocorys_, &c. (compare Pls. 92, 93, 53, 64, &c.). They may represent a true phylogenetic connection between both groups. But in these cases also the distinction is determined by the fact that the true #Plectoidea# never possess a complete sagittal ring (like the #Stephoidea#) nor a regular lattice-shell (like the #Spyroidea#, #Botryodea#, and #Cyrtoidea#).