110 PROCEEDINGS OF THE NATIONAL MUSEUM vol.81 



some; diameter, 105/x. The principal is exceedingly short and 

 slender and to it two slender terminals (occasionally three) are 

 usually attached. They are nearly straight, narrowly diverged, and 

 slightly rough, or nearly smooth on the surface. 



The second variety, form B (fig. 15, 6, <?), is nearly the same size 

 as form A, but is frequently smaller. It occurs mostly in the cho- 

 anosome, rarely intermixed with the form A in the dermal layer. 

 It is distinguished by slender principals and by weakly bifurcated 

 slender terminals. (The degree of divergence is about intermediate 

 between forms A and C.) Each short, slender, principal is provided 

 with two straight, smooth terminals, and does not form a central 

 node, as in form A. 



The last oxyhexaster, C (fig. 15, d^ /), occurring only in the 

 gastral layer, measures 76/x, in diameter. It is distinguished by 

 having very broad principals, forming a distinct central node, and 

 widely diverging terminals. Each broad principal in a spicule usu- 

 ally carries two of these widely diverging, smooth terminals. 



Besides these normal oxyhexasters, there are hemihexactinic (fig. 

 15, ?', j) and hexactinic (fig. 15, ^, h) forms in the parenchymal, 

 subdermal, and subgastral layers. They measure about SOjU in axial 

 length and have smooth-surfaced rays. 



The microdiscohexaster (fig. 15, m) is present sparsely in the gas- 

 tral layer and near the hypogastral layer. It measures 20ju, in diam- 

 eter and is provided with very delicate terminals. As its features 

 are common to the microdiscohexaster, which occurs in many mem- 

 bers of the present genus, a detailed description here is unnecessary. 



Discoctasters occur in abundance everywhere in the entire body. 

 Of them I also distinguish two varieties. They occur in different 

 quantities and show also certain differences in the manner of dis- 

 tribution and in shape. The one variety (fig. 15, 1) usually occurs in 

 the subdermal space and is much larger than the other. In diameter 

 the spicule in question varies from 190/t to 290)a. The central node 

 frequently has six more or less distinct hillocklike prominences. 

 The principals take up about one-third or less of the entire ray 

 length, measuring 32/x long, while the terminals are nearly twice as 

 long as the principals. There are five to eight terminals in a tuft; 

 occasionally as few as three. The tuft is very gently expanded dis- 

 tally, the terminals composing it being each slightly bent outward, 

 or are sometimes nearly straight. The surface of the terminals and 

 principals is smooth or microtuberculated. The terminal disks are 

 very small and pinheadlike. 



The other form (fig. 16, k) resembles that occurring in Rhabdo- 

 calyptus dawsonii. It is usually present in the subgastral and paren- 

 chymal regions; frequently in the subdermal space intermingled 

 with the former variety. It is much smaller, averaging 90/a in 



