REPORT ON THE RADIOLARIA. 969 



prolongations of the segments of the frontal ring), or three feet (one caudal and two 

 pectoral, as in Cortina and Cortiniscus), or four feet (two sagittal and two lateral, as in 

 Stephanium and Stephaniscus), or six feet (two sagittal, two pectoral, two tergal, as in 

 Semantiscus), sometimes numerous feet (as in Petalospyris and Anthocyrtis, &c.). 



The Trissocyclida represent the fourth and last subfamily of Coronida, distinguished 

 from all others in the possession of three complete rings, perpendicular one to another, 

 and of eight large gates separated by them. Two of the three rings are vertical (the 

 primary sagittal and the secondary frontal ring), the third is horizontal (the basal 

 ring). The four upper gates correspond to the four lateral gates of the preceding three 

 subfamilies ; the four lower gates are the same as the four basal gates of Semantrum (two 

 primary jugular and two secondary cardinal gates) ; therefore the Trissocyclida may be 

 derived directly from these Semantida by development of a complete frontal ring. 

 Probably the two jugular gates were originally smaller than the two cardinal, but 

 usually they have become equal. In Tristephanium (the common ancestral form of the 

 Trissocyclida) and in the closely allied Tricyclidium the four basal gates remain smaller 

 than the four lateral gates. But in two other genera, Tfissocircus and Trissocyclus, 

 the four lower or basal gates reach the same size as the four upper or lateral gates ; 

 therefore all eight gates become equal and the basal ring becomes equatorial. In the 

 most regular species of the latter genera also the three rings become perfectly equal and 

 cannot be any longer distinguished. Here the original bilateral (or dipleuric) funda- 

 mental form of the shell passes over into a regular cubic or octahedral form (with three 

 equal, isopolar axes,, perpendicular one to another). The eight large gates of the 

 Trissocyclida usually remain simple [Tristephanium, Trissocircus), but sometimes they 

 become partly closed by loose lattice-work {Tricyclidium, Trissocyclus). 



The original rings, and the secondary rods or bars, composing the loose framew^ork 

 of the Coronida are either roundish (with circular or eUi^^tical transverse section) or 

 three-edged (with triangular transverse section), rarely quadrangular or provided with 

 distorted edges. The branches or spines arising from them, are either simple or 

 branched, and offer a great variety in number, form, and disposition. The most 

 important forms are those which develop the three tj^ical basal feet of Cortina, e.g., 

 Podocoronis cortina (PL 97, fig. 2). 



The Central Capjside of the Coronida is the same as in the other Stephoidea (comp. 

 p. 937), and offers all those characteristic peculiarities of " Monopylea " which we have 

 mentioned above in the general description of the Nassellakia (p. 890). Usually it is 

 spherical or ellipsoidal, often \dolin-shaped or bilolied, with a sagittal constriction. The 

 porochora of its basal pole is in close contact -nith the l)ase of the sagittal ring. 



(ZOOL. CHAT.L. EXP. PAHT XL. — 1886.) Rr 122 



