GENERA AND aEO¥PS OP THE ECHINOIDEA. 41 



Sabfamily Pelanechinince. 



Syu. Pelanechinidcd, Grroom, 1887, Quart. Journ. Geol. Soc. 

 vol. xliii. p. 703. 



The ambulacral plates compound above the peristome, those 

 near the apex consisting of an adoral primary and six aboral 

 demi-plates ; plates near the ambitus large and pentagonal, with 

 the pairs of pores triserial(in three ranks), the demi-plates remotest 

 from the ambulacro-interradial suture, isolated. 



Genus Pelanechinus. 



Subfamily JSchinothurince. 



Ambulacral plates above the peristome ; abactinally with a 

 single large primary associated with two small demi-plates, which 

 are jDlaced in the transverse membranous areas ; actinally with 

 a primary plate associated with one or usually two demi-plates, 

 which are situated in or near the ambulacro-interradial sutural 

 line, or remote and isolated, or arrangement confused. Pairs 

 of pores triserial. Plates within the peristome low primaries, 

 each mth a pair of pores. 



Genus Echinothuria. 

 Phormosoma. 

 Asthenosoma. 



Subfamily Pelanecliinincs (supra). 

 Genus Pelanechinus, Keeping, 1878, Quart. Journ. Geol. Soc. 

 vol. xxxiv. p. 924. Groom, 1887, ibid. vol. xliii. p. 703. 

 (^Adapted.) 



Test large, circular, tumid, depressed, thin, flexible. Apical 

 system wanting. 



Ambulacra less than half the width of an interradium, still 

 broad at the peristome, beyond which they are continued. 

 Apically the plates are composed of an adoral primary and two 

 aboral demi-plates, and at the ambitus there are nine components, 

 three of which are primaries, some demi-plates isolated ; through- 

 out the poriferous zones to the peristome, the pairs of pores are 

 triserial ; beyond the peristome the ambulacral plates are simple, 

 broad, and perforated, the pair of pores in each oblique. A vertical 

 row of plain primary perforated tubercles on either side of the 

 median ambulacral suture. 



