The Echinoderm Fauna of South Africa. 297 



actinal intermediate areas are relatively smaller; but the adambulacral 

 armature is essentially the same, and the paxillae spinelets are 

 characteristically long. The specific characters are thus well shown 

 even in very small specimens. 



PTERASTERIDAE. 



This remarkable family of starfishes is well represented in South 

 African waters, since two species occur in shallow water and half a 

 dozen others are found further off shore. The family is a puzzling 

 one and the limits of the typical genus are ill-defined. So far as 

 the South African species are concerned, Retaster and Diplopteraster 

 are excellent genera, sharply set off from each other as well as from 

 Pteraster. But when all the known species are considered the line 

 between Retaster and Pteraster becomes exceedingly hard to draw 

 and that between Pteraster and Diplopteraster tends to become very 

 hazy. So far as I can see, Retaster and Diplopteraster are quite 

 distinct from each other and easy to separate, and it is strange Sladen 

 should have united them. 



Key to the South African Species of Pterasteridae. 



Armature of adambulacral plates forming transverse combs, the spinelets united 

 by a membrane. 



Adambulacral plates alike, equally prominent and equally armed; pedicels in 

 2 series. 



Paxillar spinelets united by conspicuous, ligamentous bands, forming a 

 heavy reticulum, each mesh of which forms a sharply denned area, con- 

 taining numerous small spiracles; R much exceeds 2r Retaster cribrosus. 

 Paxillar spinelets united by slender fibres, often very indistinct, not for- 

 ming a regular reticulum ; spiracles more or less scattered ; R = 2r or less. 

 R = l'5r; oral spines, 57; adambulacral spines, 5 7 



Pteraster capensis. 



R:=2r; oral spines, 4; adambulacral spines, 4 Pteraster ajfinis. 

 Adambulacral plates unlike, a more prominent regularly alternating with a 

 less prominent; latter with fewer adambulacral spines; pedicels m 4 series 



Diplopteraster multipes. 



Armature of adambulacral plates not forming webbed combs ; spinelets free. 

 Adambulacral armature of 3 spinelets. 



Supradorsal membrane not very thin; fibres connecting paxillae indistinct; 



3 oral spines on free margin of each plate . Hymenaster latebrosus. 

 Supradorsal membrane very thin ; fibres connecting paxillae conspicuous ; 



4 or 5 oral spines on sides of each plate . Hymenaster membranaceous. 

 Adambulacral armature of fewer than 3 spinelets. 



Adambulacral armature of 2 spinelets . Hymenaster lamprus. 



Adambulacral armature of a single spinelet. Hymenaster gennaeus. 



