258 THE STELLEROIDEA 



single if present. SUB-FAMILY 1. ACANTHASTERINAE, with large disc and 

 numerous rays ; numerous madreporites. Genus Acanthaster, Gerv. 

 SUB-FAMILY 2. MITHRODIINAE, with a small disc, usually five rays. One 

 madreporite ; no interbrachial septa. Armed with large scaly spines. 

 Genus Mithrodia, Gray. SUB-FAMILY 3. ECHINASTEBINAE, with a small 

 disc and five or six rays. Spines small and simple. No pedicellariae. 

 Genera Dictyaster, Mason & Alcock ; Echinaster, Mull. & Tr. ; Henricia, 

 Gray (syn. Cribrella, Ag.) ; Perknaster, Slad. ; Plectaster, Slad. SUB-FAMILY 4. 

 VALVASTERINAE, with the marginal plates bearing large valvate pedi- 

 cellariae. The disc is moderate in size, and there are five rays. Genus 

 Valvaster, Per. 



FAMILY 11. HELIASTEEIDAE. Cryptozonia with opposite ambulacral 

 ossicles and double interbrachial septa. The disc is large and bears 

 very numerous short rays. SUB-FAMILY 1. HELIANTHASTERINAE. The 

 abactinal skeleton is granular in the disc and bases of the arms ; at the 

 arm tips it is tessellate, but the plates not in contact. Arms separate 

 at their bases, so that the two sets of plates which form the interbrachial 

 septa are separated by parts of the disc. Infero-marginal plates occur 

 round the disc. Madreporite marginal. Genus Helianthaster, F. Roem. 

 This includes two Devonian species, of which only one is adequately 

 known, and is of somewhat uncertain affinities. It was originally 

 regarded as an Asteroid, but Stiirtz, in his latest description of its 

 anatomy, referred it to the Euryalidae. Stiirtz's specimens, now in the 

 British Museum, show nothing to separate them from the Asterojdea, of 

 which however they are very abnormal representatives. The ambulacral 

 plates are thin and L-shaped, but not crowded as in Heliaster, while the 

 abactinal skeleton is different. The species appears, however, to be a 

 primitive form of the Heliasteridae, in which the arms do not occupy the 

 whole margin of the disc, and are separated from one another through- 

 out ; the ambulacral plates are not crowded, so that the podia are 

 biserial. SUB-FAMILY 2. HELIASTERINAE, with reticulate, abactinal 

 skeleton and arms in contact with one another at their bases, there being 

 no interbrachial spaces. The ambulacral ossicles are crowded and the 

 pores quadriserial. Genus Heliaster, Gray. 



FAMILY 12. PEDICELLASTERIDAE. Cryptozonia with opposite ambu- 

 lacral ossicles, a small disc and narrow sub - cylindrical rays. Podia 

 biserial. The abactinal skeleton consists of narrow plates forming a 

 quadrangular network. Genera Coronaster, Per. ; Gastraster, Per. ; 

 Lytaster, Per. ; Pedicellaster, Sars. 



FAMILY 13. ASTERIIDAE. Cryptozonia with opposite ambulacral 

 ossicles. Podia quadriserial. Abactinal skeleton reticular and composed 

 of small unequal plates. Genera (including sub-genera of Asterias) 

 AntUteritUf Per. ; Asterias, Linn. ; Calvasterias, Per. ; Coscinasterias, Verr. ; 

 Cosmasterias, Slad. ; Diplasterias, Per. ; Hydrasterias, Slad. ; Leptat-terias, 

 Verr. ; Podasterias, Per. ; Polyasterias, Per. ; Pycnopodia, Stimps. ; Scler- 

 asterias, Per. ; Smilasterias, Slad. ; Sporasterias, Per. ; Uniophora, Gray. 

 The anatomy of Asterias is described on pp. 241-245. 



FAMILY 14. BRISINGIDAE. Cryptozonia with opposite ambulacral 

 ossicles ; marginal plates absent or rudimentary. Rays numerous and 



