REPORT ON THE RADIOLARIA. 1023 



The cephalis of the Zygospyrida possesss all the characteristic features which we have 

 described above as belonging to the Spyroideain general (p. 1017), and a survey of the 

 Pis. 84-87 exhibits the most important modifications of its shape (compare also PI. 95, 

 figs. 1-13). Therefore we may avoid useless repetitions by referring to the description 

 given above. We will only point out that the bilocular character of the cephalis (in oppo- 

 sition to the simple cephalis of the Monocyrtida) in the majority of Zygospyrida is apparent 

 on the first view, and that it is always demonstrated by an accurate examination of the 

 sagittal ring and its relation to the longitudinal constriction of the cephalis (compare 

 p. 1019). The basal plate or cortinar plate exhibits usually four typical pores (two smaller 

 jugular, i, and two larger cardinal, &), but this is by no means a general rule, as 

 Biitschli thought ; moreover, instead of four cortinar pores, there are frequently found 

 three or six or some other numbers (compare above, p. 1018). 



The top of the cephalis in the majority of Zygospyrida bears an apical horn, as an 

 upper prolongation of the dorsal rod of the sagittal ring ; it is often of unusual size and 

 shape (PL 85, figs. 5-11 ; PL 95, fig. 8, &c.). In several genera two lateral or frontal 

 horns are developed on both sides of the former (PL 84, figs. 9-12 ; PL 86, figs. 5-13). 

 Sometimes these two alone are present, while the original apical horn is lost by reduction 

 (PL 95, fig. 12). In other genera the apical face bears no horns ; probably they are lost 

 by reduction. 



The greatest variety of forms is produced in the Zygospyrida by the different 

 number, disposition, and shape of the feet, or the basal apophyses arising from the base 

 of the cephalis. Regarding these remarkable differences, we may distinguish eight 

 subfamilies. The common ancestral group of all are probably the Tripospyrida, which 

 possess the three typical basal feet of Cortina and Cortiniscus, an odd caudal and two 

 paired pectoral feet (PL 84). From these may be derived the Dipospyrida (PL 85) by 

 loss of the caudal foot, the Tetraspyrida by development of an odd sternal foot (PL 53, 

 figs. 7, 8, 19), and the Hexaspyrida by development of three secondary interradial between 

 the three primary perradial feet. The Pentaspyrida may have been derived from the 

 latter by loss of the sternal foot (PL 95, figs. 9-11), and the Therospyrida by loss of the 

 two sagittal feet (PL 89, figs. 5, 6). The Polyspyrida bear numerous (seven to twelve 

 or more, often twenty to thirty) basal feet, forming a corona around the cortinar plate 

 (PL 87) ; they may have been derived from the Tripospyrida or Hexaspyrida by further 

 multiplication of the feet. Finally, the Circospyrida exhibit no feet at all (PL 89, 

 figs. 7-12) ; they may be derived either from one of the preceding groups by complete 

 reduction and loss of the basal apophyses, or directly from those Semantida which 

 have no feet (Semantis, Semantrum, Clathrocircus, &c.). 



