REPORT ON THE RADIOLARIA. 



1289 



Numerous living and fossil forms of Setliocyrtida were previously described by 

 Ehrenberg, partly in his genera Dictyocephalus and Lophophcena, partly (intermingled 

 with three-jointed and many-jointed forms) in the genera Eucyrtidium and Liihocampe. 

 A larger number of new forms has been found in the Radiolarian ooze collected by the 

 Challenger, and others fossil in Barbados. Many of these Sethocyrtida are common and 

 widely distributed. When a new third joint is formed on their basal mouth, they pass 

 over into Theocyrtida. 



The cephalis is usually subspherical or hemispherical, and much smaller than the 

 thorax, the form of which exhibits all possible intermediate stages between flat, discoidal, 

 conical, cylindrical, and ovate forms. The wide open mouth becomes more and more 

 constricted, and finally closed in the Sethocapsida. The majority of the Sethocyrtida 

 may have been derived either from the Tripocyrtida, or from the Anthocyrtida by 

 reduction and loss of the radial apophyses. 



Synopsis of the Genera of Sethocyrtida. 



I. Subfamily 



Sethocorida. 

 Terminal mouth of the \ 

 thorax a simple wide 

 opening 



II. Subfamily 



Sethocapsida. 

 Terminal mouth closed 

 by a lattice-plate. ! 



Thorax conical or campanu- 

 late, gradually dilated. 



Thorax discoidal, flatly ex- 

 panded. 



Thorax cylindrical or ovate, 

 with truncate, constricted 

 or tubular mouth. 



n i. v t .1-11 



Cephalis free, not hidden in 



the thorax. 



Cephalis hidden in the ( ^ , 



, ., ., < .No horn, 



upper part of the thorax. \ 



f Shell simple, without mantle, . 572. Sethoconus. 



Shell double, with an arach- 

 noidal mantle, 



( Cephalis very large, without 

 1 horn, 



f Cephalis ( Mouth simple, 



with a * 

 single horn. ( Mouth tubular, 



Cephalis with two horns or a 

 bunch of horns, 



[ Cephalis without horn, 

 One horn, 



573. PeriararJtnium. 



574. Sethocephalus. 



575. SetJwcyrtis. 



576. Sethocorys. 



577. Loplwpluena. 



578. Dictyocephalus. 



579. Sethocapsa. 



580. Dicolocapsa. 



581. Crypiocapsa. 



Subfamily 1. SETHOCORIDA, Haeckel, Prodromus, p. 430. 



Definition. S ethocyrtida with the basal mouth of the shell open (vel Dicyrtida 

 eradiata aperta). 



(ZOOL. CHALL. EXP. PART XL. 1886.) Kr 162 



