EEPOET ON THE EADIOLARIA, 



1289 



Numerous living and fossil forms of Setliocyrtida were previously described by 

 Ehrenberg, parth' in his genera Dictyoccphahis and Lopliophcena, partly (intermingled 

 with three-jointed and many-jointed forms) in the genera Eticyrtidium and Litliocampe. 

 A larger number of new forms has been found in the Eadiolarian ooze collected 1)y the 

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

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

 over into TheocjTtida. 



The ceplialis 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 



SethocoriJa. 

 Terminal mouth of the 

 thorax a simple wide 

 opening 



f Shell simple, without manth?, . 

 Thorax conical or campanu- J 



late, gradually dilated. | Shell double, with an arach- 

 noidal mantle. 



Thorax discoidal, flatly e.x- | Ceplialis very large, without 

 panded. 1 horn, 



f Cephalis { llouth simjile, 



with a 



rp, r 1 • 1 i I single horn. I Mouth tubular, 



ihorax cylindrical or ovate, \ o \ > 



with truncate, constricted < 

 or tubular mouth. 



Cephalis with two horns or a 

 bunch of horns, 



_ Cephalis without horn. 



II. Subfamily 



Sethocapsida. 

 Terminal mouth closed 

 by a lattice-plate. 



Cephalis free, not hidden Iq | ' 



' tVio tlinrn v j ^ 



( Xo horn. 



the thorax. 



Cephalis hidden in the f ,, , 



, c ,, ., < ^0 horn, 



[ upper part of the thorax. 



•572. Sethoconus. 



573. PeriararJinium. 



574. Sethoceplialus. 



575. Setlwcyrtis. 



576. Setliocorijs. 



577. Lojjlwpluena. 



578. Dicfi/oceplialus. 



579. Setlwcapsa. 



580. Dicolocapsa. 



581. Cryptocapsa. 



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



Definition. — S e t h o c y r t i d a with the basal mouth of the shell open (vel Dieyrtida 

 eradiata aperta). 



(ZOOL. CHALL. EXP. — PART XL. — 1886.) Er 162 



