152 ART. 7. — I. IJIMA : HEXACTINELLIDA, IV. 



shaped, but still with indications of the six principals. Total 

 number of terminals, 20 at least ; some of them bifurcated at the 

 end as shown in the figure. 



DisGoctasters (PI. XII., figs. 2ö and 27) various in size, 

 measuring 106-260/'- in diameter. Secondary principals J — è as 

 long as the free part of the terminals. Number of terminals in 

 a tuft, 3-7 ; most usually 4 or 5. The discoctasters in the 

 periphery of the wall are the smallest (106-137/^ dia.), while 

 those in the deepest parts may be twice as large (generally 200- 

 260 /^ in diameter). In other respects than in size there also 

 exist some noteworthy différences between the two. 



The smaller peripheral discoctasters (fig. 25) usually show 

 distinct hump-like prominences on the central node, in the 

 middle of the spaces surrounded by every set of four secondary 

 principals. The four ridges radiating from the prominence to- 

 w^ards and into each principal are also generally but not always 

 distinct. The principals as seen in a lateral view are frequently 

 uneven in contour ; a more exact observation may show that they 

 are longitudinally ribbed throughoui the length, indicating their 

 formation by a coalescence of parts running lengthwise. PI. XL, 

 fig. 20, representing the central part of a discoctaster taken from 

 the subdermal region, demonstrates the points mentioned above, 

 besides showing the disposition of the axial cross in the central 

 node and the series of small vacuole-like spaces contained in the 

 ridges that go to form the secondary principals. The terminals 

 are obsoletely rough-surfaced ; their disc at the end is minute, 

 appearing simply like a pinhead. 



In the larger, deeply situated discoctasters (fig. 27), the 

 central node may be so large as to measure 20 /f- across. On it 



