254 THE STELLEROIDEA 



lacral ossicles and irregular marginal plates ; the upper series are often 

 covered. The abactinal skeleton is reticulate, and the plates bear large 

 tubercles. There are no valvate pedicellariae on the actinal interradial 

 areas. Genera Amphiaster, Verr. ; Asterodiscus, Gray ; Choriaster, Liitken ; 

 Gulcita, Ag. (Fig. VI.) ; Nidorellia, Gray ; Paulia, Gray ; Pentaceropsis, 

 Slad. ; Pentaceros, Schulze (Oreaster, Mull. & Tr.) ; Sphaeraster, Quenst. ; 

 Sphaerites, Quenst. 



FAMILY 11. GYMNASTERIIDAE. Phanerozonia with opposite ambu- 

 lacral ossicles and unequally developed marginal plates. Abactinal 

 skeleton tessellate, but its plates are irregular and only partially in 

 contact. The actinal interradial areas contain large plates. The whole 

 test covered with membrane. Genera Asteropsis, Mull. & Tr. Derm- 

 asterias, Per. ; Gymnasteria, Gray ; Lasiaster, Slad. ; Margincister, Per. ; 

 Porania, Gray ; Poraniomorpha, Dan. & Kor. ; Rheyaster, Slad. ; Tylaster, 

 Dan. & Kor. 



FAMILY 12. ASTERINIDAE. Phanerozonia with opposite ambulacral 

 ossicles, and with small, inconspicuous marginal plates, the axes of which 

 are convergent. Intermediate plates imbricate ; those on the abac- 

 tinal side lamelliform. Pedicellaria absent. SUB-FAMILY 1. GANERIIXAE, 

 with large marginal plates. Genera Cycethra, Bell; Ganeria, Gray; 

 Lebrunaster, Per. ; Radiaster, Per. SUB-FAMILY 2. ASTERIXIDAE, in which 

 the marginal plates do not exceed the remaining plates in size. Dermal 

 branchiae arise from any part of the abactinal surface. Genera Asterina, 

 Nardo, which has often been described as a typical Asteroid, and its embry- 

 ology carefully studied ; Disasterina, Per.; Nepanthia, Gray ; Patiria, Gray. 

 SUB-FAMILY 3. PALMIPEDINAE, with dermal branchiae confined to the 

 radial regions. Genera Palmipes, Ag. ; Stegmaster, Slad. Tremaster, 

 Verr., is also assigned to this family. 



ORDER 2. Cryptozonia, Sladen. 



Asteroidea with the marginal plates small and inconspicuous or 

 absent ; when present the upper and lower rows do not touch. Dermal 

 branchiae not limited to the abactinal surface. Ambulacral plates are 

 generally crowded and narrow. Either the ambulacral or adambulacral 

 plates are the more prominent in the oral skeleton. 



This order is characterised by three main characters: (1) The 

 insignificance of the marginal plates, whence the name Cryptozonia ; 

 (2) the occurrence of papulae or dermal branchiae beyond the abactinal 

 surface, whence the order is described as " adetopneusic '* ; and (3) the 

 crowding and narrowness of the ambulacral plates, whence the order is 

 said to be " leptostroterate." The last character is not developed in some 

 Palaeozoic genera that appear to belong to this order. 



FAMILY 1. PALAEOCOMIDAE. Cryptozonia with alternate ambulacral 

 ossicles and numerous long free actino-lateral spines. There is a web 

 supported by a reticular calcareous skeleton. The adambulacral plates 

 are large, and the spines are borne on the plates adjoining them. 

 Genus Palaeocoma, Salter. Bdellacoma, Salter, is placed by its author 

 as a sub-genus of Palaeocoma ; its affinities are doubtful, but are certainly 

 not with this family. 



