LEUCOPSACrS ORTITODOCrS. 39 



by no means everywhere uniformly and regularly developed 

 but shows at jilaces a greater or less deviation from the regular 

 pattern. 



The hei'aster>i of the species may be said to be of two kinds, 

 viz., the larger hexaetinose and the smaller hexasterous discohex- 

 asters, both found commonly in the tissues of thechoanosome. 



The hexaetinose discohexaster (PL III., fig. 16) is essentially 

 similar to that known to occur in the Euplectellid genus Corbi- 

 iella (Ij., Contrib. II.) or to the spicule figured by F. E. Schulze 

 from Ros^ella antarctica (Chall. Eep. PI. lv., fig. 8) but regarded 

 by him as perhaps extrinsic and intruded. In the present species 

 it measures 110-168 y- in axial length. The six, slender, smooth 

 and straight arms, arising from the central node in exactly the 

 same way as the rays in a regular hexactin, thicken slightly 

 towards the outer end, which bears a convexly arched, anchor-like 

 umbel of 3-5, usually 4, strong, recurved and sharply pointed 

 teeth. These are, as measured from tip to umbel center, 14/^ 

 long on an average. Special examination of the spicule mounted 

 in glycerine, showed the central cross of axial filaments in the 

 central node, the filaments not extending themselves beyond the 

 base of each arm, precisely in the manner indicated in fig. 30, 

 PI. III. 



The hexasterous diseohexaster (PI. Ill, figs. 17-20), i.e., the 

 form in which each principal bears more than one terminal in 

 distinction from the hexaetinose form, is somewhat variable as 

 regards size and certain other points, not only in different in- 

 dividuals but also in one and the same individual. It may be 

 said in general that the most usual size is 60-75/^ in diameter. 

 Jilçich short principal is supplied with a bejl-shaped, outwardlv 



