260 I. IJIMA : HEXACTINELLIDA. I. 



specimen of the spicule that ray measured 18 mm. in length and 

 fully half a millimeter in thickness at its base. It gradually 

 tapers towards the finely pointed end. The surface is profusely 

 equipped with strong, obliquely conical prickles (PL X, fig. 9) 

 which cause the shagreen-like appearance when seen with the 

 naked eye. Only small sections at the base and the end are 

 smooth. As already noticed, the coronal ray springs out quite 

 solitarily without the addition of other s]3icules, except occasional 

 rhaphides which were found adhering to its surfoce. 



The four remaining rays of the coronal oxypentactin are all 

 smooth. The inferiorly directed ray is always much shorter than 

 its opposite, coronal ray. Accompanied with comital diactins it 

 forms the longitudinal parenchymal strands visible for a short 

 distance just inside the oscular edge. Still shorter than the inferior 

 ray are the paired lateral and the unpaired outer rays. The former 

 together with compactly set diactins forms the ring-like ridge 

 just inside the origin of the coronal rays. The unpaired ray 

 extends outwards into the cuft' which it transverses without pro- 

 truding at the external edge. It thus affords a very efiicient 

 support to the cuff. Being situated just under the superior culf 

 surface, its course can be traced on that side as a whitish or a 

 slightly raised streak proceeding radially from the origin of each 

 coronal ray. 



The prodalia, both marginal and lateral, are the radially 

 directed, distal rays of very variously sized oxyhexactins, which 

 may be called the 'pvodal hexactlns (PI. X, fig. 11). These are, 

 like the similarly situated stout dermalia in R. okinoseana (pp. 2oO, 

 235), linked to the parenchymal liexactins as well as to the 

 ordinary dermalia by a gradational series of intermediate forms. 



