REPORT ON THE RADIOLARIA. 1549 



other times polygonal. From its margin small, hollow, radial spines often proceed 

 (PI. 101, fig. 9). In Dictyocha there arise from the ring two, three, four or more 

 siliceous bars or arches, M'liich form one or more bridges over one side of the ring ; 

 usually the little fenestrated shell thus produced assumes the form of a three-sided or 

 four-sided pyramid, or of a little hat with three or four meshes (PI. 101, figs. 10-14). 

 From this Dictyocha (in a restricted sense) we separate the genus Distephanus, in which 

 the little pjTamids become truncated, so that one central apical mesh (the apical or 

 upper ring) is surrounded by four, five, six or eight lateral meshes, the sides of the 

 pyramid (PI. 114, figs. 7-9). The edges of the small pyramid are formed by the same 

 number of siliceous bars arisingr from the rina: and alternatino; u-ith the meshes. Eadial 

 spines in difierent numbers and arrangements arise from the corners of the two parallel 

 rings, as well from the smaller apical as from the larger basal ring. The simple apical 

 ring of Distephanus becomes divided or fenestrated in the highest developed genus 

 of this subfamily, in Ccmnopihis (PI. 114, figs. 10-13); each pileated piece of the 

 skeleton exhibits here two rows of alternating latera^^meshes, an upper row of smaller and 

 a lower row of largjer meshes. 



The majority of Dictyochida are armed with spines or thorns, which arise in a regular 

 manner from different points of the annular or pileated pieces. In the ancestral genus, 

 Mesocena, radial spines start from the corners of the simple ring in centrifugal direction, 

 and lie horizontally in its plane. As these primary corner-spines determine the radial 

 composition of the more highly developed genera we call them perradial (lying in rays of 

 the first order). In Dictyocha and Distephanus commonly (but not c[uite constantly) these 

 perradial spines alternate with the ascending bars which bisect the sides of the basal ring; 

 these bars are therefore iuterradial (lying in rays of the second order); consec^uently also 

 the corners of the apical ring of Distephanus are interradial. The latter also often bear 

 small thorns or teeth. Other teeth frequently start in centripetal direction from the 

 lower or basal ring, on the side of the perradial spines, and frequently they are directed 

 obliquely downwards. 



In Dictyocha and Distephanus are frequently found remarkable twin pieces, composed 

 of two pileated and reticulated skeleton pieces. These are united by their basal rings 

 loosely in such a way that they form together a small fenestrated subspherical body ; 

 the union is strengthened by those small teeth of the basal rings, which are directed 

 downwards and catch one into the other (PL 101, fig. 12 ; PI. 114, fig. 8). A similar 

 twin piece has been already observed by Stohr in the fossil Distephanus rotundus, and 

 upon this was founded this genus. Since the teeth of the two opposed basal rings, 

 catching one into the other, seem to be specially adapted for the composition of those 

 smaU double pyramids, it is probable that the latter possess a special protective function 

 in these Pbleodaria, and perhaps envelop their phseodeUa or their flagellate spores (1). 

 In every case these formations are very remarkable. 



