GENEEA AND GEOPPS OF THE ECHINOrDEA. 43 



outline ; the structures of tte abactinal and actinal surfaces 

 differing. Plates numerous, thin, and surrounded by membrane, 

 imbricating more or less. 



Apical system star-shaped, large ; plates united by membrane ; 

 basals projecting into the interradial median liae, separated from 

 th.e radials by periproctal plates and membrane ; madreporite 

 large. Periproct with small spine-bearing plates. 



Ambulacra straight, broad ; plates low abactinally, high and 

 complicated aetinally ; a pair of pores in each plate, and a pair 

 in each of the two small accessory plates along the adoral or the 

 ambulacro-interradial suture ; buccal plates continuous with, those 

 of the ambulacra, low, broad, pore-penetrated, overlapping. 

 Primary tubercles of the interporiferous areas few, small, larger 

 at the margin, more numerous aetinally, perforate, scrobiculate ; 

 plates with granules. 



Interradia with numerous low and broad plates,partlybut broadly 

 overlapping from below upwards, or connected all along the 

 transverse sutures by membrane. Tubercles larger than in the 

 ambulacra, smaller and most numerous aetinally. 



Peristome moderate, branchial incisions small, external branchiae 

 distinct. Perignathic girdle slender. Spines short, longest and 

 most numerous aetinally, where some are capped with a hoof-shaped 

 process, others club-shaped or like long and short needles, striated 

 and cylindrical in section, may be sheathed. Pedicellarise some 

 long and blunt-headed, others with very open valves, and many 

 tridactyle and blunt-headed. Actinal tentacles disciferous, and 

 the abactinal are pointed and branchial. 



The plates, especially of the ambulacra, often seem to be split up 

 in a remarkable manner. Spheridia may exist. 



Becent. N. Atlantic to Azores; Caribbean Sea, and to the 

 N., Japan, Philippines, Sandwich Islands, Low Archipelago, 

 E. Pacific, Australia, Juan Fernandez to Chili. 120 to 2750 

 fathoms. 



G-enus Asthenosoma, Grube, 1868, JaJiresb. d. Schles. Ges. f. 



Vaterl. Cult. p. 42. A. Agassiz, 1872, Bevision, p. 272 ; EcJi. 



of ' BlaJce ' JExped. 1883, p. 29. Ludwig, 1880, Zeits. f. wiss. 



Zool. vol. xxxiv. P. Sf F. Sarasin, 1888, Frg. Nat. For. auf 



Ceylon, Bd. i. Heft 3, p. 129. 

 Syn. Calveria, "Wy. Thomson, 1873, Phil. Trans. Eoy. Soc. 

 vol. clxiv. pt. 2, p. 737. 



