GENERA AND QEOFPS OF THE ECHINOIDEA. 7 



ambulacrum. TiarecMnus, so ably described by Loven after 

 jSTeumayr, is unique and must enter an order of its own. And, 

 fiDally, the exocyclic Echinocystites comes into tbe order Cysto- 

 cidaroida. 



It is certainly supremely interesting to find jaws and teeth in 

 these old forms and to be able to classify, thanks to Sir Wy. 

 Thomson, an exocyclic gnathostome amongst the Palaeozoic 

 Echinoidea. 



Classification. 

 Subclass PAL^ECHINOIDEA. (Page 5.) 

 Order I. BOTHRIOCIDAROIDA. 



Genus Bothriocidaris, Schmidt. 

 Order II. PERISCHOECHINOIDA. 



Family Arch^ocidarid^. 



Genus Lepidocentrus, J. Miiller. 



Koninckocidaris, DoUo & Buisseret. 

 Ferischodomus, McCoy. 

 ArchcBocidaris, McCoy. 

 Lepidocidaris, Meek & Worthen. 

 LepidechinuSf Hall. 

 Palcsechinus (Scouler), McCoy (pars). 

 Mhoechinus, W. Keeping. 

 Family Melonitid^. 



Genus Melonites, Norwood and Owen. 

 Oligoporus, Meek & Worthen. 

 Lepidesthes, Meek & Worthen. 

 Hybochinus, Worthen & Miller. 

 Pholidocidaris, Meek & Worthen. 

 Order III. PLESIOCIDAROIDA. 



Genus TiarecMnus, Neumayr. 

 Order IV. CYSTOCIDAROIDA. 



Genus Echinocystites, Wy. Thomson, I86L 



Order I. BOTHEIOCIDAEOIDA, 



F. Schmidt, 1874 ; Zitfel, 1876-80. 

 Test regular, more or less spherical, solid ; interradia with only 

 one vertical row of plates which do not imbricate ; ambulacra 

 with two vertical rows of plates ; plates united at their edges. 

 Periproct in the central apical system. Peristome actiual, central. 

 Jaws ? 



