1242 



THE VOYAGE OF H.M.S. CHALLENGER. 



The majority of the Anthocyrtida may be derived from the Polyspyrida (Petalo- 

 spyris, &c.) by reduction of the cephalis and loss of the sagittal ring, as was suggested by 

 Biitschli (1882, loc. cit.). But another part may also have arisen from the Tripocyrtida, 

 by interpolation of secondary radial apophyses between the three primary perradial 

 apophyses. The cephalis in this family is developed in all possible degrees, from one of 

 a considerable size to one very much reduced. If it becomes perfectly lost, the Cyrto- 

 ealpida arise. 



Synopsis of the Gene of Anthocyrtida. 



L Subfamily 



Sethophormida. 

 Terminal mouth of the 

 thorax a simple wide 

 opening. 



II. Subfamily 



Sethophsenida. 

 Terminal mouth closed 

 by a lattice-plate. 



f Shell flat, campanulate or 

 nearly discoidal (cephalis 

 without horn), 



Kadial ribs smooth (rarely 

 thorny) enclosed in the 

 wall of the thorax (cepha- 

 lis commonly small, with- 

 out horns). 



Shell ovate, with constricted 

 mouth (without horn), 



Meshes of 

 the network 

 simple, 



Shell 



slender 



pyramidal, 



with straight 



ribs. 



Radial ribs thorny (rarely 

 smooth) prolonged into 

 free terminal feet (cepha- -I. 

 lis commonly large, with | 



Meshes fenes- 

 trated by 

 secondary lat- 

 ticework, 



Meshes closed 

 by spongy 

 framework, . 



Shell not enveloped by arach- 

 noidal network, 



one or more horns). 



Shell enveloped by arachnoidal 

 [ network, . 



Thorax with lateral apophyses (four to six or more wings), . 

 Thorax with terminal apophyses (four to six or more feet), . 



558. Sethophormis, 



559. Sefhamphora. 



560. Setliopyramis. 



561. Pledopyramis. 



562. Spongopyramis. 



563. Accunthocarys. 



564. Arachnocorys. 



565. Anthocyrtonm. 



566. AntJwcyrtis. 



567. Antboajriium. 



568. Anthocyrtidium. 



569. Carpocanium. 



570. SeihopluKiia. 



571. Clistophcena. 



