xxxviii THE VOYAGE OF H.M.S. CHALLENGER. 



Subfamily 2. Pythonasterinje, Sladen, 1888. 



Pterasteridse having a stellate form, with greatly produced attenuate and cylindrical 



rays. Supradorsal membrane absent. No actino-lateral spines, and no segmental 



apertures. Abactinal spines short, in sheathed fascicules, not forming pedicellate 



paxillse. 



Genus 1. Pythonaster, Sladen. 



For a Synopsis of the Subfamilies and Genera included in the Family Pterasteridas, 

 see p. 469. 



Family VI. Echinasterid^e, Verrill, 1871 (1867), emend. 



Cryptozonate Asterids with a reticulate abactinal skeleton, often irregular, formed of 

 small imbricating plates, bearing isolated or grouped spines. Disk sometimes large but 

 usually small, with the rays elongate and often subcylindrical. With single interbrachial 

 septa. Actinostomial margin defined by adambulacral plates. Ambulacral tube-feet 

 biserial. Pedicellarias rarely present (only known in two genera) ; monomorphic ; never 

 forcipiform. 



Subfamily 1. Acanthasteein^;, Sladen, 1888. 



Echinasteridse with a large disk and numerous rays. Armed with large isolated spines 

 covered witb membrane beset with calcareous granules. Numerous madreporiform bodies. 

 Forficiform pedicellariae present. 



Genus 1. Acanthaster, Gervais. 



Subfamily 2. Mithrodiiisle, Viguier, 1878. 



Echinasteridse with a small disk and usually five elongate rays. Armed with large 



spines beset with scales or asperities. One madreporiform body. No pedicellarias present. 



No interbrachial partitions. 



Genus 1. Mithrodia, Gray. 



Subfamily 3. Echinasterin.e, Viguier, 1878. 



Echinasteridai with a small or medium-sized disk and five or six rays. Spinulation 

 small and simple ; spinelets isolated or grouped. No pedicellariae present. 



Genus 1. Cribrella (Agassiz), Forbes. 



Genus 2. Perknaster, n. gen. 



Genus 3. Echinaster, Midler and Troschel. 



Genus 4. Plectaster, n. gen. 



