ECHINOIDEA. SPATANGOIDA. 



245 



the enlarged peristomial plate (labrum) of the posterior interradius. 

 They are usually sand-burrowers and the tube-feet show considerable 

 diversity. 



In the young state the form approaches that of the regular urchins in 

 the position of the mouth and the form of the ambulacra. Jurassic to 

 the present time. The Spatangidae are first found in the Cretaceous. 



Section 1. ASTERN ATA. 



Shell oval, mouth central or sub-central, without sternum and fascicles ; 

 ambulacra all alike, simple or petaloid. Apical system compact or 

 elongate. Interradii some or all with a single peristomial plate. With- 

 out plastrons, with or without floscelles. Through the Echinoneidae 

 they are related to the regular forms and through the Cassidulidae to 

 the Clypeastrids. 



Fam. 1. Echinoneidae. Ambulacra simple, all alike, without petals. 

 Mouth central, without floscelle. With four perforated basal plates. 

 Mostly begin in Cretace- 

 ous, but a few in the }]} 

 Jurassic. Echinoconus 

 Breyn., f, Cretaceous ; 

 Lanieria Duncan, f ; Echi- 

 noneus van Phel., f and r, 

 Caribbean Sea, Australia, 

 Zanzibar, etc. ; Amblypy- 

 gus L. Ag., f ; Caratomus 

 L. Ag., f ; Pygaulus L. 

 Ag., f ; Pyrina Desm., f, 

 Jurassic to Eocene ; 

 Nucleopygus L. Ag., f ; 

 Anorthopygus Cotteau, f ; 

 Haimea Mich, f ; Oligo- 

 pygus De Lor., f ; Echi- 

 nobrissus Breyn. (Nucleo- 

 lites Lm.), f ; Anochanus 

 Grube, r ; Botriopygus 

 d'Orb. f ; Ilariona Dames, 

 f. 



Fam. 2. Cassidulidae. 

 Ambulacra petaloid or 

 not, closed or open below. 



Peristome with floscelle (Fig. 173). With four genital pores, the basals 

 are sometimes fused ; the madreporite much extended. Jurassic to 

 present day. Cassidulus Lamk., f ; Echinanthus Breyn., f ; Studeria 

 Dune. (Catopygua L. Ag.), f and r; Clypeus Klein, f ; Pygurus d'Orb., 

 f ; Eckinolampas Gray, f and r ; Conolampas A. [Ag. r ; Neolampas 

 A. Ag., r ; Rhynchopygus d'Orb., r. 



Section 2. STERNATA. 



Peristome excentric anteriorly. Sternum well developed. Anterior 

 ambulacrum different from the rest (except in Ananchytidae). Fascioles 

 present or absent. Without floscelle. 



Fam. 1. Collyritidae. Without floscelle ; apical system elongate 

 (Fig. 162), disjunct ; the two posterior radials being separated by a con- 



FIG. 173. Oral region of Cassidulus pacifieus showing 

 phyllodes (after Lov6n from Delage). b mouth ; I-V 

 radii numbered. 



