vm EGHINODERMATA-^SYSTEMATIG REVIEW 293 



the shell is very Hat : Sculella (Fig. 234), Echimdiscus, Micojk, Mii//ita (Fig. 235), 

 Rofi'/ri, Ai-achiuiid-s, etc. (extant and fossil). 



Fig. 2S5.~Mellita testudinata? from the oral side (original). 



Order 5. Spatangoida. 



llouth central, suh-central, or on the anterior edge of the oral surface of the test 

 Anus outside the apical system, in the posterior interradius. External gills, jaws, 

 teeth, and perignathous apophysial ring wanting. Sphferidia present. The ambu- 

 lacra generally form apical petaloids. The test is bilaterally symmetrical, arched, 

 often heart-shaped. 



Sub-Order 1. Cassiduloidea. 



Fam. 1. Eohinoneidae : Echinoconus, Echinoneiis, OUyopyyus, Eclmiolrissus, etc. 

 (extant and fossil). Fam. 2. Cassidulidse : Cassidulus, Cato2')ijgus, Cbjjxus, Pygurus, 

 Echinolampas, etc. (mostly iossA). Fam. 3. CoUyiitidse : CoUyrUes,Dysaster, etc. 

 (fossil). Fam. 4. Plesiospatangidse : Eolam-pas, Archiacia, etc. (fossil). 



Sub-Order 2. Spatangoidea. 



Fam. 1. Anan-chytidse : Echinocoi-ys, Holastcr, Scmijmeustes, Oardiaster, Uir- 

 cltiims, Cystechiiius, Calymiw, etc. (the last three genera extant, the rest fossil). 

 ' Fam. 2. Spatangidse — Group 1, Adetes : Isaster, EcMnospatagus, Heterolampas, 

 Hriiiipatagus, etc. (almost exclusively fossil) ; Group 2, Prynmadetes : Hcmiastcr, 

 Ffi/jriaa, Linthia, ScMzastcr (Fig. 236), Agassizia (extant and fossil) ; Group 3, 

 PrymnodeBmia : Micrastnr, Brissus, Spiatangmnorpilia, Brissopsis, Spatmigus, Palceop- 

 ii'.ustes (Fig. 237), Echinocard him, Luvrnia, etc. (extant and fossil); Group 4, 

 Apetala : fknicopatagus, Pa/ccoirissus, Accste, Aeropic, etc. (extant and fossil). 



