12 ART. 7. 1. IJIMA : HEXACTINELLIDA, IV. 



seen under ii high magnifying power, is rough on account of 

 microtubercles (PL I., fig. 12). In some cases, tlie roughness of 

 the surface is more pronounced than in others, the microtubercles 

 being then visible as minute reverted prickles or barbs. The 

 convex terminal disc, when well developed as is generally the 

 case, exhibits comparativelv strong recurvate marginal jirongs, 

 Ü-G in number. Occasionally the ]irougs are minute or quite 

 obsolete ; they may even be ajiparently wanting, in which case 

 the terminals appear as if ending bhuitly, iu all probability 

 rejiresenting a developmental stage |)revious to the formation of 

 the terminal prongs. In rare instance I liave seen small and 

 delicate oxyhexaster-like forms, which I consider to be likewise 

 an early stage in the genesis of the discohexaster. 



One individual (Mus. No. 436) of the species from ( )utside 

 Okinose, which I have studied with special tlioroughuess as 

 regards the spiculation, requires to be here particularly mentioned. 

 In it I have discovered, though certainly as rare al)normalities, 

 cases of the discohexastei' in which some — not all— of the termi- 

 nals are bent outwards and backwards, directly after their origin 

 from the principal, in a semicii'cle or in a comma-like manner, 

 apparently with no dcliiiitc rule as to the I'elative orientation of 

 the [)lane of curvature. They arc not unlike the peculiarly 

 twisted oxyhexasters figured by F. E. Schulze from Jkithydonis 

 f<j)uiosiis (C'hall. Ivep., JM. UX., fig. 9) and from llhahdocalyptus 

 iiioIIU (/. c, I'l. LXIV., figs. 10, 11').— As repi-esentatives of 

 jioinial discohexasters in the same s[»ecimen I have shown three 

 in my Contribution III., 1*1. \., figs. 1-:!. Some of the small- 

 est, such as is shown in /. c. fig. 3, are distinguished l)y the 

 fact that the numl)er of terminals is somewhat more numei-ous 

 than usual, there l)eing six or more of them to each principal. 



