368 Annals of the South African Museum. 



Key to the South African Families of Echini. 



Mouth and periproct central and opposite. 

 Primary tubercles perforate. 

 Ambulacral plates simple. 



Peristome covered with numerous small plates. . Cidaridae. 



Peristome with only ten large, buccal plates . Aspidodiadematidae. 

 Ambulacral plates compound, at least orally. 



Test more or less flexible, or at least not very rigid ; periproct more 

 or less leathery ; spines slender, hollow. 



Peristome not covered by ambulacral plates Centrechinidae. 



Peristome covered by five double columns of perforated ambul- 

 acral plates . ... Echinothuridae. 



Test rigid ; periproct well plated ; spines stout, solid . Pedinidae. 

 Primary tubercles imperforate. 



Large, permanent, suranal plate, similar to those of oculo-genital ring, 

 present . . . . Saleniidae. 



Suranal plate, if present, small, or if large, not at all like those of oculo- 

 genital ring. 



In midzone, every four or five ambulacral plates fused together and 

 grown over by one large primary tubercle . Stomopneustidae. 



Ambulacral plates in midzone, not thus fused together. 

 Ambitus circular. 



Periproct covered by 4 (rarely 3,5 or more) similar, trian- 

 gular plates .... Arbaciidae. 



Periproct covered by several or many dissimilar, and usually, 

 irregularly arranged plates. 



Ambulacral plates made up of 3 elements; ambitus at 

 or bt-low equator. 



Test, at least abactinally or in midzone, more or 



less sculptured or ornamented with deep pits or 



furrows . . . Temnopleuridae. 



Test not sculptured, pitted or furrowed Echinidae. 



Ambulacral plates made up of 4 or more elements; or 



if only 3 are present, ambitus above equator 



Strongy locentro tidae. 



Ambitus elliptical . . . Ecldnometridae. 



Mouth central or anterior ; periproct posterior, often on oral surface. 

 Mouth central, with jaws. 



Auricles (of perignathic girdle) separate ; test not diecoidal ; genital 

 pores 5 . . . . . . . . Clypeastridae. 



Auricles fused into a single piece. 



Test not discoidal and with no lunules or marginal slits. 



Petals more or less perfect; madreporic pores numerous; test 

 flattened, moderate or large .... Laganidae. 



Petals reduced, often rudimentary; only one madreporic pore; 

 test small, 5 8 mm. long, rarely up to 15 mm., but often 

 relatively high ..... Fibulariidae. 



