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 aud loss of the sagittal ring, as was suggested by 

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

 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- 

 calpida arise. 



1. Subfamily 



Sethophormida. 

 Terminal mouth of the 

 thorax a simple wide 

 opening. 



Synopsis of the Genera of Antlwcyrtida. 



Shell flat, . campanulate or 

 nearly discoidal (cephalis 

 without horn), 



Shell ovate, with constricted 

 mouth (■without horn), 



Radial ribs smooth (rarely 

 thorny) enclosed in the 

 wall of the thorax (cepha- ■ 

 lis commonly small, with 

 out horns). 



Shell 



slender 



pyramidal, 



with straight 



ribs. 



Eadial ribs thorny (rarely 

 smooth) prolonged into 

 free terminal feet (cepha- 

 lis commonly large, with 

 one or more horns). 



]\Ieshes of 



the network 

 simple, 



Meshes fenes- 

 trated by 

 secondary lat- 

 ticework. 



Meshes closed 

 by spongy 

 framework, . 



Shell not enveloped by arach- 

 noidal network. 



Shell enveloped by arachnoidal 



network. 



No ribs in 



the thorax. 



Peristome 



with free 



terminal 



feet. 



Cephalis 



well- 

 developed, - 



with an 

 apical horn 



Feet 



terminal, 



without 



separate 



peristome. 



Six feet, 



Nine feet. 



Twelve or more 

 feet. 



Feet subterminal, outside the 

 constricted peristome. 



II. Subfamily 



Sethopha;nida. 

 Terminal mouth closed " 

 by a lattice-plate. 



Cephalis rudimentary, hidden in the upper 

 part of the thorax, without horn, . 



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

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



558. Sethophormis. 

 5-59. Sethainpliora. 



560. Setkopyramis. 



561. Plectopyramis. 



562. Spiongopiyramis. 



563. Accmthocwys, 



56 L Araehnocorys. 



565. Anihoryrtoma. 



566. Anthocyrtis. 



567. Antliocyrtium. 



568. Atitlioeyrtidium. 



569. Carpocanimn. 



570. SetJiojJhama. 



571. Clistopilucna. 



