166 PEor. p. M. Duncan's eeyision of the 



VI. 



Order V. The Spatangoida. Suborder Cassiduloidea. Tlie Family Echino- 

 neidse, Subfamilies and Genera. Genera incertae sedis. Family Cassidulidse 

 and its Alliances and Genera and Subgenera. Family Collyritida and Genera. 

 The Family Plesiospatangidag and Genera. 



Order V. SPATANGOIDA (p. 25). 

 Suborder Cassiduloidea. 

 Spatangoidea, 



I. Suborder Cassiduloidea. 



Exocyclic nodostomes with a transverse or an oblique elliptical 

 or irregularly shaped or pentagonal peristome ; witb or without 

 "floscelles." Apical system either compact or elongate. Ambu- 

 lacra abactinally simple, petaloid or subpetaloid, usually similar. 

 Interradia, some or all, with a single peristomial plate ; the pos- 

 tero-lateral areas symmetrical actiually, without any fusion of 

 plates ; no plastrons. Periproct in the posterior interradium. 



I. Family EchinoneidjE. 



Subfamilies Echinoconince, Echinoneinee, Oligopygince, Echino- 

 brissince. 



II. Family Cassidulid^. I T 



III. „ CoLLYRITlDiE. 1 Cf (p 



IV. „ PLESIOSPATANGID.ffi;. /ff 



I. Family Echinoneid^. 



Cassiduloidea with variously-sized tests, ovoid or subpentagonal 

 in marginal outline ; tall, subconical, or subhemispherical, or low 

 and tumid dorsally ; tumid and rarely flat actinally. Apical 

 system central, compact or subcompact, with four perforated 

 basal plates. Ambulacra similar, moderate in width to narrow, 

 dorsally apetalous or subpetaloid, rarely tending to close. Pores 

 in simple pairs or rarely in oblique triplets actinally ; no floscelle. 

 Tentacles homoiopodous. Peristome oblique or transverse and 

 elliptical, rarely symmetrical ; the number of interradial peri- 

 stomial plates variable. Periproct actinal, marginal or supra- 

 marginal. 



This Family is subdivided into four subfamilies. 



